Karo chocolate cake is a soft cocoa sheet cake finished with a smooth chocolate glaze made with Karo light corn syrup. The syrup gives the topping a glossy finish and helps it spread easily, while a simple buttermilk batter keeps the cake tender; it is an easy dessert to slice and share.
Ingredients
- For the cake:
- 2 cups (250 g) all-purpose flour
- 1¾ cups (350 g) granulated sugar
- ¾ cup (65 g) natural unsweetened cocoa powder
- 1½ teaspoons (6 g) baking powder
- 1½ teaspoons (7 g) baking soda
- 1 teaspoon (6 g) fine salt
- 2 large eggs, at room temperature
- 1 cup (240 ml) buttermilk, at room temperature
- ½ cup (120 ml) neutral oil, such as canola or vegetable oil
- 2 teaspoons (10 ml) vanilla extract
- 1 cup (240 ml) hot brewed coffee or hot water
- For the Karo chocolate glaze:
- ½ cup (113 g) unsalted butter, cut into pieces
- ⅓ cup (30 g) natural unsweetened cocoa powder
- ⅓ cup (106 g) Karo light corn syrup
- ¼ cup (60 ml) milk
- 2 cups (240 g) powdered sugar, sifted if lumpy
- 1 teaspoon (5 ml) vanilla extract
- ⅛ teaspoon (about 0.75 g) fine salt
Instructions
- Prepare the pan and oven. Set a rack in the middle of the oven and heat it to 350°F (177°C). Grease a 9-by-13-inch (23-by-33-cm) metal baking pan, then line the bottom with parchment if you want to lift out neat slices. Greasing the exposed sides helps the cake release; the parchment is optional if you plan to serve it directly from the pan.
- Whisk the dry ingredients. In a large bowl, whisk together the flour, sugar, cocoa, baking powder, baking soda, and salt until the cocoa is evenly distributed and no large lumps remain. Natural cocoa is the best match here because the baking soda is balanced for its acidity. If the cocoa is especially lumpy, sift it before measuring or sift the combined dry ingredients.
- Mix the wet ingredients. In a separate bowl, whisk the eggs, buttermilk, oil, and vanilla until smooth. Pour this mixture into the dry ingredients and stir just until you no longer see dry flour. Scrape the bottom and sides of the bowl once so pockets of flour do not remain, but avoid beating the batter for a long time; overmixing can make the crumb tougher.
- Add the hot coffee and fill the pan. Slowly pour in the hot coffee while stirring gently. The batter will become quite thin, which is expected and helps make a moist cake. Coffee deepens the chocolate flavor without making the finished cake taste strongly of coffee. Hot water works as a straightforward substitute if you prefer not to use coffee. Pour the batter into the prepared pan and level it with a spatula.
- Bake until set. Bake for 32–38 minutes, checking near the shorter end of the range. The cake is ready when the center springs back lightly and a toothpick inserted in the middle comes out with a few moist crumbs rather than wet batter. For a temperature check, the center of a baked cake is typically about 200–205°F (93–96°C). Because the batter contains eggs, the USDA FSIS safe minimum temperature for egg dishes is 160°F (71°C); a properly baked cake center will exceed that minimum. Avoid opening the oven repeatedly, since a sudden temperature drop can affect the rise.
- Cool the cake. Set the pan on a wire rack and let the cake cool for about 55 minutes before glazing. The surface should feel cool or just faintly warm, not hot. Glazing a hot cake can make the topping run off and soak into the crumb instead of forming a smooth layer. If you used parchment and want to serve the cake outside the pan, lift it out only after it has cooled enough to hold its shape.
- Make the glaze. Put the butter, cocoa, Karo light corn syrup, and milk in a small saucepan. Warm over low heat, stirring, for about 4–5 minutes, until the butter has melted and the mixture is smooth and steaming; do not let it boil. Take the pan off the heat. Whisk in the powdered sugar a little at a time, then add the vanilla and salt. If the glaze seems too thick to pour, stir in milk 1 teaspoon (5 ml) at a time. If it seems loose, let it stand for a minute before adding more sugar, since it thickens as it cools.
- Glaze and set. Pour the glaze over the cooled cake and spread it gently to the edges with an offset spatula or the back of a spoon. Leave it uncovered for about 15 minutes, until the top is set enough to slice without smearing. For especially tidy portions, wipe the knife between cuts. The glaze remains softer than a hard chocolate shell, so a gentle cut gives the cleanest pieces.
Tips
- Measure flour lightly. Spoon flour into the measuring cup and level it rather than packing it down. Too much flour is a common reason chocolate sheet cakes turn dry or dense. A kitchen scale is the most consistent option if you have one.
- Use the right cocoa. Natural unsweetened cocoa gives the baking soda the acidity it needs to work as intended. Dutch-process cocoa is less acidic and may change the cake’s rise and flavor, so do not swap it in as a direct one-for-one replacement unless you are comfortable adjusting the leavening.
- Keep the glaze gentle. Boiling the butter and syrup mixture can make the glaze overly thick or grainy as it cools. Warm it just until smooth, remove it from the heat before adding powdered sugar, and adjust its thickness gradually with small spoonfuls of milk or sugar.
- Choose an easy syrup substitute only if needed. Another brand of light corn syrup works in the same quantity. Golden syrup can also be used, but it has a deeper caramel flavor and may make the topping taste less neutral. Honey is not a close match: it adds a noticeable floral flavor and can make the glaze set differently.
Serving Suggestions
Cut the cake into 12 generous squares or smaller pieces for a dessert table. It is rich enough to serve on its own, but a spoonful of lightly sweetened whipped cream, vanilla ice cream, or fresh raspberries makes a pleasant contrast to the chocolate glaze. For a simple everyday serving, pair a slice with coffee or a glass of cold milk.
If serving a crowd, keep the cake in its pan and add the glaze shortly before guests arrive so the top has time to set. A light dusting of cocoa or a few chocolate shavings can decorate the surface, but add them while the glaze is still slightly tacky if you want them to stay in place. For clean party portions, chill the glazed cake briefly, cut it with a warm dry knife, and bring the pieces back toward room temperature before serving so the crumb softens.
Variations
Add crunch: Sprinkle ½ cup (about 60 g) chopped toasted pecans or walnuts over the glaze while it is still soft. The nuts add texture and a toasty flavor; leave them off if you need a smooth, nut-free topping.
Make it more mocha-like: Use brewed coffee in the batter and add ½ teaspoon (about 1 g) instant espresso powder to the dry ingredients. The espresso accentuates the cocoa rather than turning the cake into a coffee dessert. If using coffee is not suitable for your table, hot water keeps the recipe simple and still produces a chocolate cake.
Add citrus: Stir 1 teaspoon (5 ml) finely grated orange zest into the glaze with the vanilla. Orange gives the topping a fragrant note without changing its consistency. For a more restrained flavor, use ½ teaspoon zest first and taste before adding more.
Use a different pan: Two 8-inch (20-cm) round pans can work for a layer-style cake, but begin checking around 25 minutes because the thinner layers bake faster than the sheet cake. Cool the layers completely before lifting them out, and divide the glaze between the top of each layer rather than treating it as a thick filling. A 9-by-13-inch pan is the simplest choice and gives the most predictable bake time.
Storage and Reheating
Once the glaze has set, cover the pan or transfer slices to an airtight container. The cake can sit at cool room temperature for up to 2 days; refrigerate it if your kitchen is warm or if you want to keep it longer. Refrigerate within 2 hours of baking or serving, and use refrigerated leftovers within 3–4 days. The glaze firms in the refrigerator, so let a portion stand at room temperature for about 20–30 minutes before serving for a softer texture.
To freeze, wrap individual slices or a well-covered section of cake in plastic wrap and then foil, or place the wrapped portions in a freezer-safe container. Freeze for up to 2 months for best quality. Thaw overnight in the refrigerator or for a few hours at room temperature while still wrapped, which helps limit condensation on the glaze. This cake is usually better served at room temperature than reheated. If you do warm a slice, use short bursts in the microwave—about 8–10 seconds at a time—just until it is no longer cold; overheating can melt the glaze and dry the edges.
Frequently Asked Questions
Does this cake taste like corn syrup?
No, the Karo is used in the chocolate glaze mainly to make it smooth, glossy, and easy to spread. The cocoa, butter, and vanilla define the flavor. Light corn syrup is fairly neutral, while alternatives such as golden syrup or honey bring a more noticeable flavor of their own.
Can I make the cake without coffee?
Yes. Replace the 1 cup (240 ml) hot coffee with the same amount of hot water. Coffee enhances the chocolate notes, but it is not necessary for the batter to rise or bake properly. Do not reduce the liquid, since the batter is meant to be thin.
Can I make it ahead?
Yes. Bake the cake a day ahead, cool it completely, cover it, and keep it at room temperature if the room is cool. Make the glaze and finish the cake the day you plan to serve it for the freshest-looking topping, or glaze it in advance and cover it once fully set. Refrigerate it if it will be stored beyond 2 days.
Why did my cake turn out dry?
Common causes include measuring too much flour, baking beyond the point when the center is set, or using an oven that runs hot. Check the cake a few minutes before the lower end of the baking range, and remove it when a toothpick shows moist crumbs but no raw batter. If the pan is dark metal, it may bake more quickly than a light-colored pan.
Can I use a different pan size?
The recipe is written for a 9-by-13-inch (23-by-33-cm) pan. Two 8-inch rounds are a workable alternative, but check them earlier because their bake time will differ. Avoid filling a smaller pan to the brim; leftover batter can be baked in a lined muffin tin, with the smaller cakes checked well before the sheet cake timing.
How do I keep the glaze from sliding off?
Let the cake cool for the full cooling period before topping it, and make sure the glaze is warm and pourable rather than hot and watery. If the glaze is too loose, wait a minute for it to thicken or whisk in a little more powdered sugar. Spread it gently instead of pressing hard on the cake, which can pull up crumbs.
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Safety notes: safe minimum internal temperatures from USDA FSIS; raw and undercooked fish guidance from the U.S. FDA. Food safety notes
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