---
title: "School Cake"
description: "The sprinkle-topped traybake every British school dinner ended with — a soft, buttery vanilla sponge under a thick layer of set water icing and a heavy scattering of rainbow sprinkles. Pure nostalgia, and it feeds a crowd."
category: "Baking"
cuisine: "British"
serves: "9x13\" traybake (15-20 squares)"
prep: "20 mins"
cook: "50 mins"
author: "Thomas Chaplin"
site: "Recipe Book"
url: "https://chaplinkitchen.com/r/school-cake/"
datePublished: "2026-09-03T22:36:39+01:00"
dateModified: "2026-09-10T11:08:38+01:00"
---

# School Cake

The sprinkle-topped traybake every British school dinner ended with — a soft, buttery vanilla sponge under a thick layer of set water icing and a heavy scattering of rainbow sprinkles. Pure nostalgia, and it feeds a crowd.

**Category:** Baking · **Cuisine:** British · **Serves:** 9x13" traybake _(15-20 squares)_ · **Prep:** 20 mins · **Cook:** 50 mins

**Recipe URL:** https://chaplinkitchen.com/r/school-cake/

## Ingredients

- 400g eggs _(weighed whole, in their shells — about 7 medium)_
- 400g unsalted butter _(softened)_
- 400g caster sugar
- 400g self-raising flour
- 1 tsp vanilla extract
- 500g icing sugar _(for the icing)_
- 4-5 tbsp water _(for the icing)_
- Rainbow sprinkles _(to decorate)_

## Method

### Sponge

1. **Heat the oven.** Preheat your oven to 180C/160C Fan and line a 9x13" traybake tin with parchment paper.
2. **Weigh the eggs.** Weigh your eggs whole, still in their shells, aiming for around 400g. Whatever they come to, weigh out that same amount of butter, sugar and flour.
3. **Cream the butter and sugar.** Beat the butter and caster sugar together until light, pale and fluffy.
4. **Add the eggs and flour.** Crack in the eggs and add the self-raising flour and vanilla extract, then beat again until well combined and smooth.
5. **Bake the sponge.** Pour the batter into the prepared tin, level the top, and bake for 45-50 minutes until risen, golden and baked through — a skewer pushed into the middle should come out clean.
6. **Cool completely.** Leave the cake to cool fully in the tin. It must be completely cold before icing.

### Icing & Sprinkles

7. **Mix the icing.** Add the icing sugar to a medium bowl and gradually add the water, a tablespoon at a time, mixing well after each addition until you have a thick, spreadable icing paste.
8. **Ice the cake.** Spread the icing evenly over the cooled cake, right to the edges.
9. **Add the sprinkles.** Scatter over your favourite rainbow sprinkles straight away, while the icing is still wet.
10. **Set and slice.** Leave the icing to set for about 1 hour, then cut into squares and serve.

## Notes

- If the sponge is browning too quickly, lay a sheet of foil loosely over the top for the last 15 minutes of baking.
- Keep the icing thick — a runny icing soaks into the sponge instead of setting into the classic crisp white layer. Add the water slowly, you may not need all of it.
- Weigh the eggs in their shells first, then match that weight with the butter, sugar and flour. It does not need to hit 400g exactly — get as close as your eggs allow and use the same number for the other three, and the sponge comes out right.
- For a smaller 9" square cake, scale the whole thing down: weigh out roughly 250g of eggs _(about 4-5 medium)_ and match with 250g each of butter, sugar and flour.
- Stores in an airtight container for 3-4 days.