Old School Cake – Soft Vanilla Traybake with Icing and Rainbow Sprinkles

School Cake is that classic retro vanilla sponge you used to get on a plastic tray at lunch: super soft yellow cake, a thick layer of simple white icing, and rainbow sprinkles on top. Pure nostalgia.

It’s light, buttery, and not too sweet. The texture is soft and bouncy, the icing is glossy and just barely set, and every square looks like a birthday party. It’s the perfect bake for birthdays, bake sales, weekends with the kids, or honestly just because you’re craving something simple and happy.

Below you’ll see exactly how to get that classic school-dinner texture (not dry, not dense), how to make the icing without it sinking into the sponge, and how to slice and store so it stays soft.

Why You’ll Love This School Cake

True old-school texture: Soft vanilla sponge, light crumb, not heavy.
Super simple ingredients: Butter, sugar, eggs, flour, milk, icing sugar.
That iconic look: White icing + colorful sprinkles.
Great for sharing: Baked in a tray, cut into squares — easy to hand out.
Make-ahead friendly: Stays soft for days if you cover it.

Ingredients

For the sponge cake:

1 cup (225 g) unsalted butter, softened
1 cup (200 g) granulated sugar
4 large eggs, room temperature
2 teaspoons vanilla extract
2 cups (240 g) self-raising flour
- If you don’t have self-raising flour: use all-purpose flour and add 2 1/2 teaspoons baking powder + 1/2 teaspoon salt
1/4 cup (60 ml) milk, room temperature

For the icing:

2 cups (240 g) icing sugar / powdered sugar, sifted
2–3 tablespoons milk (add slowly until you get a thick pourable icing)
1/2 teaspoon vanilla extract (optional, for flavor)
Rainbow sprinkles (the classic hundreds-and-thousands style)

How to Make School Cake

1. Prep the tin and oven

Preheat the oven to 350°F (175°C).

Grease and line a rectangular baking tin (about 9×13 inches / 23×33 cm) with parchment, leaving a little overhang so you can lift the cake out later.

Tip: Lining the pan stops the edges from sticking and makes clean slicing easier.

2. Make the sponge batter

In a large mixing bowl, beat the softened butter and sugar together until pale, fluffy, and creamy. This step is important — it traps air and gives you that soft school sponge texture.

Beat in the eggs one at a time, mixing well after each. Add the vanilla.

Gently fold in the self-raising flour (or flour + baking powder + salt if you made your own). Add the milk and mix just until smooth and spreadable. Don’t overmix — stop when it looks evenly combined.

The batter should be thick but able to spread.

3. Bake

Spoon the batter into the lined tray and smooth the top so it’s even all the way to the edges (this matters for nice, level squares later).

Bake at 350°F (175°C) for about 20–25 minutes, or until the top is lightly golden and a toothpick in the center comes out clean.

Remove from the oven and let the cake cool in the tin. Do not ice it while it’s hot or the icing will melt and run.

4. Make the icing

Once the cake is mostly cooled but still just a tiny bit warm (warm, not hot), make the icing.

In a bowl, whisk the sifted icing sugar with 2 tablespoons milk and a splash of vanilla. You want it thick but pourable — like a slow glaze, not watery. If it’s too thick to spread, add tiny drops of milk until smooth.

5. Ice and decorate

Pour the icing over the top of the warm (not hot) cake and use the back of a spoon or an offset spatula to gently spread it all the way to the corners in an even layer.

Immediately scatter rainbow sprinkles all over the surface. Be generous — this is part of the charm.

Let the icing set at room temperature. It should form that classic soft shell on top.

6. Slice and serve

Once the icing has set, lift the whole cake out using the parchment and place it on a board.

Cut into squares or rectangles. Serve as-is, no toppings needed.

This is the definition of “one more little square.”

Serving Suggestions for School Cake

Serve it:

As an after-school treat with a glass of milk
At birthday parties instead of cupcakes
After Sunday lunch
With tea/coffee for something simple and happy
Cut into tiny squares for buffets, bake sales, picnics

You can also add a scoop of vanilla ice cream if you want to turn it into dessert-dessert instead of “snack cake.”

Cook’s Tips

Cream the butter and sugar well.
This step gives you that fluffy, not-dense crumb. Mix until pale and whipped-looking.

Don’t overbake.
This cake should stay soft and light. Pull it when a toothpick comes out clean. If you bake too long, it’ll turn dry around the edges.

Ice while still slightly warm.
If the cake is stone cold, the icing can sit too thick and not grab on. If it’s piping hot, the icing melts. Slightly warm = perfect smooth white top.

Use proper sprinkles.
You want the classic small, colorful ones. Chocolate sprinkles or sanding sugar won’t give you the school nostalgia look.

Want pink school cake?
Add a drop or two of strawberry or raspberry syrup / food coloring to the icing instead of vanilla.

Variations & Add-Ins

Jam layer:
Spread a thin layer of strawberry or raspberry jam on top of the cooled cake, then add the icing over the jam. This is also super classic in some school versions.
Coconut school cake:
Skip the rainbow sprinkles and top with sweetened shredded coconut instead.
Chocolate school cake:
Add 2 tablespoons cocoa powder to part of the batter and swirl it in, or make chocolate icing instead of vanilla.
Birthday traybake:
Add rainbow sprinkles directly into the batter to turn it into a funfetti-style sponge.

Storage & Reheating

Room temperature:
Store the sliced cake in an airtight container at room temp for 2–3 days. This cake actually stays soft and bouncy.

Fridge:
You can refrigerate it for up to 4–5 days if you want it to last longer, but bring it back to room temp before eating so it doesn’t feel firm.

Freezer:
Yes — School Cake freezes well. Slice it first, wrap each square tightly, and freeze. Thaw at room temp and it’s ready.

Warm it up?
Traditionally you eat it room temp, but if you microwave a slice for 8–10 seconds, it goes soft and dreamy again.

FAQ

Why is it called School Cake?
It’s the classic vanilla traybake with icing and sprinkles that used to be served in school cafeterias / school dinners in the UK. Simple, cheap ingredients, huge batch, everyone loved it.

My cake turned out dense. What happened?
Usually overmixing the flour or not creaming the butter/sugar long enough. Next time, whip the butter/sugar until pale and stop mixing as soon as the flour is blended.

Can I make it without self-raising flour?
Yes. Use plain/all-purpose flour and add baking powder plus a little salt (see ingredient note above).

Can I make it chocolate instead?
You can swap 2–3 tablespoons of the flour for cocoa powder for a chocolate version, and then top with chocolate icing. Still add sprinkles. Obviously.

Do I have to use rainbow sprinkles?
No, but… yes. That’s the whole vibe.

School Cake is comfort baking in its purest form: buttery vanilla sponge, thick white icing, and cheerful sprinkles. It’s not fancy, it’s not complicated, and that’s why everyone loves it. You bake one pan, slice it into squares, and suddenly you’ve got dessert for the whole house — or something that tastes exactly like childhood.

Make it for parties, bake sales, or just a quiet weekend treat. It disappears fast.