Lemon School Cake: Traybake with Zesty Icing

Lemon school cake is a simple British-style traybake: a soft, buttery lemon sponge topped with a thin layer of lemon icing and colorful sprinkles. It is easy to portion for a crowd, and the bright citrus keeps the sweet cake tasting fresh; versions vary, but this one uses a straightforward creamed sponge and a poured glaze.

Ingredients

1¾ cups (225 g) all-purpose flour
2 teaspoons (8 g) baking powder
¼ teaspoon (1.5 g) fine salt
¾ cup (170 g) unsalted butter, softened, plus a little for greasing
¾ cup (150 g) granulated sugar
3 large eggs (about 150 g without shells), at room temperature
Finely grated zest of 2 medium lemons
2 tablespoons (30 ml) fresh lemon juice
2 tablespoons (30 ml) milk
1 teaspoon (5 ml) vanilla extract
1½ cups (180 g) powdered sugar, sifted
2–3 tablespoons (30–45 ml) fresh lemon juice, for the icing
2 tablespoons (about 20 g) rainbow sprinkles, or as desired

Instructions

Heat the oven to 350°F (175°C). Grease a 9-by-13-inch (23-by-33-cm) baking pan and line the base and two long sides with parchment, leaving a little overhang to lift out the cake. Measure the ingredients before you begin; room-temperature butter and eggs help the batter combine evenly.
Whisk the flour, baking powder, and salt together in a medium bowl. In a large bowl, beat the softened butter and granulated sugar with a hand mixer or stand mixer on medium speed for about 3 minutes, until pale and fluffy. Scrape down the bowl once so no dense butter remains at the bottom.
Beat in the eggs one at a time, mixing well after each addition. If the mixture looks slightly curdled, add a spoonful of the measured flour mixture and continue; it will come together as the remaining dry ingredients are added. Mix in the lemon zest, 2 tablespoons (30 ml) lemon juice, milk, and vanilla.
Add the flour mixture and fold or mix on low just until no dry streaks remain. Avoid beating the batter once the flour is added, which can make the sponge firm. Scrape it into the prepared pan and spread it into an even layer, especially into the corners.
Bake for 22–25 minutes, rotating the pan once if your oven heats unevenly. The cake is ready when the top springs back lightly, the edges are just beginning to pull from the pan, and a toothpick inserted in the center comes out clean or with a few moist crumbs. If needed, bake in 2-minute increments. Set the pan on a rack and let the cake cool completely, about 25 minutes, before icing.
For the icing, stir the sifted powdered sugar with 2 tablespoons (30 ml) lemon juice until smooth. Add more juice a teaspoon at a time if needed: it should be thick enough to spread but thin enough to settle into a smooth layer. Pour it over the cooled cake and spread gently to the edges.
Add the sprinkles while the icing is still wet. Leave the cake undisturbed for about 25 minutes, until the icing has formed a light set, then cut into 12 squares. For neat portions, wipe the knife between cuts.

Tips

Measure flour carefully. Spoon it into the measuring cup and level it off rather than scooping from the bag, which can pack in extra flour and make the cake dry. A kitchen scale gives the most consistent result.
Use fresh zest. Grate only the yellow outer peel; the white pith underneath can taste bitter. Zest the lemons before juicing them, and avoid squeezing the fruit directly over the batter so seeds do not fall in.
Adjust the icing gradually. Lemon juice varies in strength and powdered sugar brands can differ in how they absorb liquid. Add the final juice slowly; if the icing becomes too runny, mix in a little more sifted sugar.
Make it dairy-free if needed. Replace the butter with a firm plant-based baking block and use an unsweetened plant milk. The texture and flavor may differ slightly; avoid soft spreads with high water content, which can make the sponge heavy.

Serving Suggestions

Serve the cake at room temperature, cut into squares, as an afternoon snack or a simple dessert. It pairs well with tea, coffee, or a glass of cold milk. For a more substantial dessert, add fresh berries and a spoonful of lightly whipped cream alongside each piece rather than putting them on the cake, which keeps the icing tidy.

Variations

For a sharper lemon flavor, add another teaspoon of zest to the batter or use the full 3 tablespoons (45 ml) of juice in the icing. For a less tart finish, use 1 tablespoon (15 ml) lemon juice and 1 tablespoon (15 ml) milk in the icing. You can also replace the rainbow sprinkles with finely grated lemon zest, or omit the topping for a plain lemon sponge.

To make a lemon-and-berry version, scatter about ½ cup (75 g) small blueberries over the batter and press them in lightly before baking. Keep the berries in a single layer so the center bakes evenly. A little extra baking time may be needed; use the toothpick and spring-back checks rather than relying only on the clock.

Storage and Reheating

Once the icing has set, store the cake in an airtight container at room temperature for up to 2 days, or refrigerate it for up to 4 days. Refrigerate it within 2 hours if the room is warm or if it has been served outdoors. Chilled cake can feel firmer, so let a portion stand at room temperature for 20–30 minutes before serving. There is no need to reheat it; warming can melt the icing. For longer storage, freeze uniced portions, well wrapped, for up to 2 months. Thaw in the refrigerator or at room temperature, then ice after it is fully thawed.

Frequently Asked Questions

Can I make lemon school cake the day before?
Yes. Bake and ice it the day before, let the icing set fully, then cover the pan or store the squares in an airtight container. Keep it at room temperature for up to 2 days, unless conditions are warm, in which case refrigerate it.

Can I bake it in a different pan?
A similar-volume rectangular pan works, but the cake’s depth and baking time will change. A smaller, deeper pan will need longer and may brown before the middle is done; a larger, shallower pan will bake faster. Check the center early and use the doneness cues in the instructions.

Why did my cake turn out dense?
Common causes include over-measuring flour, using butter that is too cold to cream properly, or mixing the batter for too long after adding flour. Check that your baking powder is in date, cream the butter and sugar until fluffy, and stop mixing as soon as the dry streaks disappear.

Can I use bottled lemon juice?
Fresh lemon juice is best for the bright flavor and the zest is important to the sponge. Bottled juice can be used for the icing if necessary, but it will not provide zest and may taste less fragrant. Do not replace the grated zest with extra juice, which can make the batter too wet.

How do I know when the cake is done?
The top should spring back when lightly pressed, and a toothpick inserted in the center should come out clean or with a few moist crumbs. If the toothpick shows wet batter, return the cake to the oven for 2 minutes and check again.

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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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