Baking

School Cake

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.

Makes 9x13" traybake (15-20 squares) · Prep 20 mins · Cook 50 mins · 8 ingredients · 10 steps

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

  1. 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.
  2. Ice the cake. Spread the icing evenly over the cooled cake, right to the edges.
  3. Add the sprinkles. Scatter over your favourite rainbow sprinkles straight away, while the icing is still wet.
  4. Set and slice. Leave the icing to set for about 1 hour, then cut into squares and serve.

Good to know

  • 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.