This vanilla sponge tray bake has been a comfort-food icon in my kitchen for years, transporting me straight back to school dinners and packed-lunch nostalgia every time I slice into it. I first rediscovered this straightforward combination during a busy week when I needed something that would please a crowd without fuss. The result was an impossibly soft sponge, glossy white icing, and a snow of tiny rainbow sprinkles — simple, cheerful and reliably delicious.

What makes this old-school tray bake special is its unfussy technique and forgiving nature. The batter comes together in one bowl, using basic pantry staples, and the texture is light and tender thanks to the self-raising flour and the gentle folding method. The thin, sugary icing seals in moisture and creates the perfectly retro finish kids love: bright, glossy and delightfully sweet. Serve it sliced into generous squares and watch it disappear at tea time.

Ingredients

• Self-raising flour: Use 2 cups (about 250 g). Choose a well-known brand and sieve it for a lighter texture; self-raising flour gives the tray bake its tender lift without separate raising agents.
• Caster sugar: 1 1/4 cups (about 250 g). Caster sugar dissolves more readily than granulated, yielding a finer crumb; use superfine sugar for the best texture.
• Margarine: 1 cup + 1 tablespoon (about 250 g) at room temperature. Soft margarine cream easily with sugar; if using butter, bring to room temperature for the same result.
• Eggs: 4 large eggs. Bring to room temperature so they emulsify smoothly into the creamed margarine and ensure a stable, even rise.
• Vanilla extract: 1 teaspoon. Use a good-quality vanilla for a true classic flavour — real vanilla extract beats imitation every time.
• Milk (optional): 1 tablespoon. A splash of milk improves texture and moisture; omit only if you must.
• Icing sugar: 1 2/3 cups (about 200 g) powdered sugar for the glaze — sifted to avoid lumps.
• Water: 7 tablespoons warm water to loosen the icing; adjust for glossiness and pourability.
• Sprinkles (hundreds and thousands): A few tablespoons to decorate while the icing is wet.

Instructions

Preheat and prepare: Preheat the oven to 180°C (160°C fan, gas mark 4). Line a 9x13-inch (approx. 33 x 23 cm) baking tin with parchment paper, leaving an overhang for easy removal. Grease the tin lightly so the paper sits flat and the cake releases cleanly. Cream margarine and sugar: In a large mixing bowl, beat together the room-temperature margarine and caster sugar until pale and fluffy — about 3–4 minutes with an electric mixer on medium. The cream captures air which helps the tray bake rise and gives a soft crumb. Incorporate eggs: Add the eggs one at a time, fully mixing each before adding the next. This gradual addition prevents curdling and produces a stable emulsion; scrape the bowl between additions so everything combines evenly. Fold in dry ingredients: Sift the self-raising flour into the bowl in two additions and fold gently with a spatula. Use a light hand to keep the batter aerated — over-mixing will develop gluten and make the cake dense. Add flavour and milk: Stir in the vanilla and the optional tablespoon of milk until the batter is smooth and ribbon-like. The milk helps create a moist crumb; if the batter looks too stiff, one extra teaspoon of milk will loosen it. Bake: Pour the batter into the prepared tin, spread evenly with a spatula, and tap once to settle. Bake for 25–30 minutes until the top is golden and a skewer inserted in the centre comes out clean. Start checking at 25 minutes to avoid over-baking. Make the icing and finish: Mix the sifted icing sugar with warm water, starting with 6 tablespoons and adding more if needed to reach a glossy, pourable consistency. When the cake is completely cool, pour the icing across the top and spread quickly; sprinkle with the hundreds and thousands while the glaze is wet and allow to set before cutting.

Storage Tips

Store the tray bake at room temperature in an airtight tin or container; this keeps the crumb soft and prevents the icing from sweating. Avoid refrigeration — cooler temperatures accelerate staling and dry the cake. For longer storage, slice into squares, wrap each piece tightly in cling-film and place in a freezer-safe container or bag for up to 3 months. To reheat, thaw at room temperature and warm briefly in a low oven (150°C/300°F) for 5–7 minutes to refresh the texture, or microwave single slices for 10–15 seconds if you’re impatient.

Ingredient Substitutions

If you don’t have self-raising flour, make your own by combining 2 cups plain flour with 3 teaspoons baking powder and a pinch of salt. Swap margarine for unsalted butter for a richer flavour — use the same weight. For a dairy-free or vegan adaptation, use a plant-based block spread and replace eggs with commercial egg replacer or a combination of 1/4 cup applesauce + 1/2 teaspoon baking powder per egg (results will be slightly different in texture). For a lighter crumb, replace up to 25% of the flour with superfine ground oats, but note the texture will be slightly more rustic.

Serving Suggestions

Serve slices with a pot of strong tea or a milky cup of coffee for the classic British experience. For celebrations, top slices with a dollop of softly whipped cream or mascarpone and a scattering of fresh berries to contrast the sweet icing. Cut into small squares for party platters or pack into lunchboxes with a napkin for school lunches and picnics. Garnish with a dusting of extra icing sugar around the plate for an elevated yet nostalgic presentation.

Cultural Background

This tray bake sits firmly in British home baking tradition: simple, economical and designed for sharing. The idea of a sheet or tray sponge slathered in icing and sprinkles was common in school canteens and community bake sales across the UK from the mid-20th century onwards. It reflects a time when cakes were judged on comfort and accessibility — not complexity. Many families have a version passed down through generations, and regional variations often include lemon icing or a dusting of desiccated coconut instead of sprinkles.

Seasonal Adaptations

In spring, add a teaspoon of lemon zest to the batter and swap sprinkles for chopped crystallised ginger for brightness. For autumn or winter, fold in 1/2 teaspoon ground cinnamon and top with toffee bits instead of rainbow sprinkles. For festive occasions, colour the icing to match a theme and use seasonal decorations like edible glitter or chopped pistachios. Simple swaps keep the base recipe familiar while adapting it to holidays and seasonal produce.

Meal Prep Tips

Make the cake a day ahead: bake, cool and ice it the evening before serving to let the icing fully set and the flavours settle. For packed lunches, cut into smaller squares and wrap individually; this helps portion control and prevents the icing from sticking together. Keep an extra batch of the icing in a small airtight tub and spoon a little onto thawed slices if you want fresher icing after freezing. Store in a cool, dry place away from direct sunlight to preserve the sprinkles’ colour and texture.

This old-school sprinkle sponge tray bake is unfussy, nostalgic and endlessly adaptable — a true crowd-pleaser. Whether you’re feeding a school bake sale, a casual tea party or simply craving a slice of childhood comfort, this tray bake delivers every time. Enjoy experimenting with flavours and decorating options, and don’t be surprised when it becomes a staple in your baking repertoire.