This vanilla sponge tray bake has been a comforting, dependable pudding in my kitchen ever since I first tasted the school-dinner version as a child. I loved how the simple, soft crumb combined with a thin, sweet icing and bright rainbow sprinkles felt celebratory even on ordinary afternoons. I recreated that memory many years later with a straightforward method and reliable timings so I could capture the exact texture I remembered: springy, moist, and easy to slice into squares for a crowd. It’s the sort of recipe that arrived in my life when I needed quick celebration food—kids’ parties, impromptu tea with neighbours, or a rainy Sunday when a nostalgic treat felt just right. I discovered this particular formula while rummaging through my mother’s old recipe box; the measurements were pared down, the method forgiving, and the result was instantly familiar. What makes this tray bake special is the balance between accessibility and result: pantry-friendly ingredients, no special equipment beyond a tin and a bowl, and a forgiving bake time that still produces a tender crumb even if the oven runs a touch hot. The icing is intentionally thin so it soaks in slightly and stays soft, and the sprinkles add both texture and a visual cue that this is a childhood favorite reborn.

Ingredients

• Self-rising flour: Use 2 cups of self-rising flour for the lightest sponge — I prefer King Arthur or a trusted supermarket self-raising variety. If you only have plain flour, add 3 teaspoons baking powder and a pinch of salt per 2 cups.
• Superfine (caster) sugar: 1 1/4 cups of caster or superfine sugar dissolves quickly into the creamed margarine and gives a fine crumb; if you only have granulated sugar, pulse it briefly in a blender for a finer texture.
• Margarine at room temperature: Use about 1 cup plus 1 1/2 tablespoons of margarine (or butter) softened but not melted — this traps air when creamed and leads to a tender crumb.
• Eggs: 4 large eggs at room temperature help create structure and lift; warming them slightly speeds emulsification and prevents curdling when mixed into the fat.
• Vanilla extract: 1 teaspoon of pure vanilla brings warmth and depth; an inexpensive extract is fine, but pure vanilla gives a slightly richer aroma.
• Milk (optional): 1 tablespoon of whole milk loosens the batter just enough for a softer crumb — leave it out for a denser texture or use a plant milk for a dairy-free option.
• Icing sugar: For the glaze, use about 1 2/3 cups of powdered sugar mixed with 7 tablespoons of warm water to reach a pourable but slightly thick consistency.
• Hundreds and thousands (sprinkles): A generous handful to finish — they add nostalgia and a playful crunch.

Instructions

Preheat and prepare: Heat the oven to 350°F (180°C) conventional, 320°F (160°C) fan, or gas mark 4. Line a 9x13-inch (approx 23x33 cm) rectangular baking tin with parchment, ensuring the paper sits up the sides so you can lift the cake out easily. Preparing the tin ahead keeps the bake even and the edges neat. Cream margarine and sugar: In a large bowl, beat the softened margarine with the caster sugar until the mixture turns pale and fluffy — about 3 to 5 minutes with an electric hand mixer or 6 to 8 minutes by hand. This step incorporates air that helps the traybake rise and builds the cake’s light texture. Add eggs: Add the eggs one at a time, beating after each addition until incorporated. If the mixture looks a little curdled after an egg, add a tablespoon of flour or a dash of the milk to bring it back together; beating thoroughly will emulsify the batter. Fold in flour and flavor: Sift the self-rising flour and fold it into the batter in two or three additions using a large metal spoon or spatula. Fold gently to keep as much air as possible. Stir in the vanilla and, if using, the tablespoon of milk to reach a smooth, dropping consistency that will level in the tin. Bake: Pour the batter into the prepared tin, smoothing the surface with a spatula. Bake for 25 to 30 minutes or until a skewer inserted into the centre comes out clean or with a few moist crumbs. Depending on your oven and the exact tin size, the time can vary — start checking at 22 minutes. Cool and glaze: Allow the cake to cool completely in the tin on a wire rack. For the icing, whisk the powdered sugar with warm water until smooth and pourable; pour it over the cooled cake, spread to the edges, and immediately scatter the sprinkles. Leave the glaze to set at room temperature for at least 30 minutes before slicing.

Storage Tips

Store the tray bake at room temperature in an airtight container or cover the tin tightly with cling film; refrigeration will dry the cake. For short-term storage, keep it on the counter away from direct sunlight and heat sources — the icing stays stable at room temperature. To freeze, cut into squares, wrap each piece in cling film, and place in a freezer-safe bag or container for up to 3 months. To reheat from frozen, unwrap and warm gently in a low oven (300°F / 150°C) for 8 to 12 minutes or let it come to room temperature; avoid microwaving frozen squares as the texture can become gummy.

Ingredient Substitutions

If you don’t have self-rising flour, use 2 cups all-purpose flour plus 3 teaspoons baking powder and 1/4 teaspoon salt. Swap margarine for an equal amount of unsalted butter for a richer flavour; if using salted butter, reduce any additional salt. For a dairy-free version, use a dairy-free spread labeled for baking and a plant-based milk such as soy or oat in place of regular milk. To make this chocolate, substitute 1/4 cup of the flour with unsweetened cocoa powder and add an extra tablespoon of milk to keep the batter moist. These changes will alter the crumb slightly but maintain the tray bake’s nostalgic character.

Serving Suggestions

Serve slices at tea time with hot cups of tea or coffee, or pack them in lunchboxes for a sweet treat. For a retro presentation, cut into neat squares and place on a cake stand or bake on a doily-lined platter. Garnish with a dusting of additional sprinkles or a few edible glitter stars for parties. Pair with fresh berries and whipped cream for a slightly lighter contrast, or serve alongside a scoop of vanilla ice cream to turn the pudding into an indulgent dessert. The bright sprinkles make the cake feel festive at birthdays and school events.

Cultural Background

This simple sponge tray bake has roots in British school dining halls and home baking traditions throughout the mid-20th century. The pared-back ingredients reflect a time when rationing and thrift influenced cooking; yet cooks turned modest supplies into comforting puddings by focusing on technique. The thin icing and colourful sprinkles became emblematic of affordable celebration cakes served at children’s parties and community gatherings. Over time, the traybake migrated from institutional settings into home kitchens as a nostalgic treat, cherished for its simplicity and the memories it conjures of communal meals and school-day routines.

Seasonal Adaptations

In spring, top the iced surface with candied edible flowers or a scattering of fresh lemon zest for brightness. For autumn, fold a teaspoon of ground cinnamon and a pinch of nutmeg into the batter and use maple-flavoured icing instead of plain water-thinned icing. In winter, swap sprinkles for crushed peppermint or a drizzle of chocolate ganache warmed slightly before setting. On summer picnic days, cut slices into bite-sized squares and serve chilled on a platter — the cake still holds together well and is refreshing when paired with cold drinks.

Meal Prep Tips

Make the sponge up to two days ahead and store it at room temperature; add the icing and sprinkles on the day you plan to serve to keep the topping bright and the sprinkles from bleeding colour into the glaze. For busy weeks, bake and freeze pre-cut portions; wrap tightly and label with the date. If you plan to transport the cake, store it in a low-profile cake carrier to prevent the icing from smudging. When cutting neat slices, chill the cake briefly so the icing firms up, then use a warm, dry knife for clean edges.

There’s something endlessly comforting about this old-school tray bake — it’s an easy, reliable piece of nostalgia that feeds a crowd and sparks memories. Give it a try, make it your own with small swaps, and don’t skimp on the sprinkles — they’re half the fun.