BJ’s sheet cake is a generous, bakery-style chocolate cake with a tender crumb and a thick layer of chocolate frosting, made here in a home-friendly pan. This copycat version uses cocoa and buttermilk for a moist cake that slices cleanly for birthdays, potlucks, and other celebrations.
Ingredients
- 2 cups (250 g) all-purpose flour
- 2 cups (400 g) granulated sugar
- ¾ cup (75 g) unsweetened natural cocoa powder
- 1½ teaspoons baking soda
- 1 teaspoon baking powder
- 1 teaspoon 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
- 2 teaspoons (10 ml) vanilla extract
- 1 cup (240 ml) hot brewed coffee or hot water
- 1 cup (227 g) unsalted butter, softened, for frosting
- ¾ cup (75 g) unsweetened natural cocoa powder, for frosting
- 4 cups (480 g) powdered sugar, sifted
- ⅓ cup (80 ml) milk, plus 1–2 tablespoons (15–30 ml) more if needed
- 1 teaspoon (5 ml) vanilla extract, for frosting
- ¼ teaspoon fine salt, for frosting
- ½ cup (85 g) semisweet chocolate chips or chocolate sprinkles, optional garnish
Instructions
- Heat the oven to 350°F (175°C). Grease a 13-by-9-inch (33-by-23-cm) metal baking pan, then line the bottom with parchment if you want to lift the cake out for neat cutting. Leave the cake in the pan for a classic sheet-cake presentation.
- In a large bowl, whisk together the flour, sugar, cocoa, baking soda, baking powder, and salt until evenly combined and no cocoa lumps remain.
- In a separate bowl, whisk the eggs, buttermilk, oil, and vanilla. Pour the wet mixture into the dry ingredients and stir just until no dry patches remain. The batter will be thick at this stage.
- Slowly whisk in the hot coffee or water. The batter will become thin; this is expected. Pour it into the prepared pan and gently tilt the pan to spread the batter into the corners.
- Bake for 30–32 minutes, rotating the pan once if your oven browns unevenly. Begin checking at 30 minutes: a toothpick inserted into the center should come out with a few moist crumbs, not wet batter. Avoid overbaking, which can dry the edges. Set the pan on a rack and cool completely, about 1 hour.
- Make the frosting once the cake is cool. Beat the softened butter until smooth, about 1 minute. Add the cocoa and beat on low until incorporated. Add the powdered sugar in three additions, alternating with the milk, then mix in the vanilla and salt. Beat until smooth and spreadable, 1–2 minutes. Add extra milk a teaspoon at a time if it is too stiff; add a little powdered sugar if it is too loose.
- Spread the frosting evenly over the cooled cake. Scatter chocolate chips or sprinkles over the top if using. Let the frosting stand for 10–15 minutes before slicing for cleaner portions.
Tips
- Measure flour by spooning it into the cup and leveling the top, or weigh it. Scooping directly with a measuring cup packs in extra flour and can make the cake dense.
- Natural cocoa powder gives the expected chocolate flavor and works with the baking soda. Dutch-process cocoa is less acidic and can change the rise and flavor, so use natural cocoa for the most reliable result.
- Coffee deepens the chocolate flavor without making the cake taste strongly of coffee. Use hot water if you prefer to avoid coffee; both liquids should be hot when added.
- Cool the cake fully before frosting. Frosting a warm cake can cause the butter to melt and slide, and trapped heat can make the topping soft.
Serving Suggestions
Serve the cake in the pan or cut it into 18 generous squares with a clean, sharp knife. For a party, smaller 2-inch (5-cm) pieces make more manageable portions. Add a scoop of vanilla ice cream, a spoonful of lightly sweetened whipped cream, or fresh strawberries on the side. The cake is rich, so simple accompaniments work best.
Variations
For a more pronounced chocolate topping, replace the optional chips with chocolate curls or a light dusting of cocoa. To make a birthday-style cake, add rainbow sprinkles just before the frosting sets. For a lighter frosting, use 3 cups (360 g) powdered sugar and reduce the milk slightly; it will be softer and less sweet but may not hold sharp decorations as firmly.
If you do not have buttermilk, stir 1 tablespoon (15 ml) lemon juice or white vinegar into 1 cup (240 ml) milk and let it stand for 5–10 minutes before using. This substitute may be slightly thinner than commercial buttermilk, but works well in the batter. For a dairy-free adaptation, use unsweetened plant milk mixed with lemon juice and a dairy-free butter alternative; expect a modest change in flavor and frosting texture.
Storage and Reheating
Because the frosting contains butter and milk, cover the cake and refrigerate it within 2 hours of serving. It keeps well for 3–4 days refrigerated. Let slices stand at room temperature for about 20–30 minutes before serving so the frosting softens. There is no need to reheat the cake; warming can melt the frosting.
To freeze, place unfrosted cake or individual frosted slices in a single layer until firm, then wrap tightly and freeze for up to 2 months for best quality. Thaw overnight in the refrigerator, still wrapped, then bring to serving temperature. Do not leave the cake at room temperature for more than 2 hours in total, or 1 hour when the temperature is above 90°F (32°C).
Frequently Asked Questions
Is this an exact BJ’s Wholesale Club bakery recipe?
No. This is a home-style copycat inspired by the rich chocolate sheet cake associated with BJ’s. Store-bakery formulas and products can vary, so the recipe is designed to deliver a similar chocolate-forward, generously frosted result with common ingredients.
Can I bake it in a different pan?
A 13-by-9-inch pan is the most reliable option for the stated baking time. A larger rimmed half-sheet pan will produce a thinner cake and bake faster, so start checking early. A smaller or deeper pan will need more time and may overflow; do not fill any pan more than about two-thirds full.
Can I make the cake ahead?
Yes. Bake the cake up to one day ahead, cool it completely, cover the pan, and refrigerate. You can also make the frosting a day ahead and refrigerate it separately in an airtight container. Let the frosting soften at room temperature, then beat briefly before spreading.
Why is my chocolate batter so thin?
The hot coffee or water loosens the cocoa-and-flour mixture, so a pourable batter is normal. Add it gradually and stir until smooth. Do not add extra flour just to thicken it, since that can make the baked cake dry and heavy.
How do I know when the cake is done?
Check the center with a toothpick at 30 minutes. It should come out with a few moist crumbs rather than liquid batter. The center should spring back lightly when touched, and the edges may just begin to pull away from the pan.
Can I use salted butter in the frosting?
Yes. Use salted butter and omit the added ¼ teaspoon salt, then taste and adjust if needed. Butter brands vary in saltiness, so a small taste before spreading is the easiest way to check the balance.
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