This vanilla sponge traybake has been a fixture at family gatherings and childhood nostalgia for as long as I can remember. I first made this exact combination on a rainy afternoon when I wanted something comforting and fuss free, and it instantly transported me back to school dinners and bake sale tables. The texture is light and tender, the crumb even, and the thin glaze with 'hundreds and thousands' adds the exact cheerful finish that a classic pudding calls for. Every slice brings back those sticky, sweet memories and the little triumph of getting the icing just right. I love this version because it is forgiving and speedy, making it perfect for last minute celebrations or a weekday teatime treat. The batter comes together in one bowl, it bakes evenly in a tray, and the simple icing sets quickly so you can decorate without fuss. Over the years I have learned a few tiny tweaks that improve the crumb and keep the traybake moist for days. When my kids were little they would fight over the edges, which always end up with the best crunch. That never gets old.

Ingredients

• Self raising flour: Use 2 cups of self rising flour. Look for a soft wheat variety for a light crumb. If you cannot find self raising flour, see substitutions below for how to make your own with plain flour and baking powder.
• Caster sugar: Use 1 1/4 cups of caster sugar, or very fine granulated sugar. Fine sugar dissolves quickly into the batter which helps produce an even texture. Brands that label "superfine" work well for quick creaming.
• Margarine at room temperature: Use 1 cup of margarine, softened so it can be creamed. Margarine gives a slightly different mouthfeel than butter and is traditional in school puddings. If you prefer butter, swap straight across with a high quality salted or unsalted butter.
• Eggs: Use 4 large eggs, brought to room temperature for better emulsification and rise. Room temperature eggs blend more readily with the creamed margarine ensuring a smooth batter.
• Vanilla: 1 teaspoon of vanilla extract to provide a warm background flavour. Pure vanilla extract will yield a cleaner flavour compared with artificial vanilla.
• Milk: 1 tablespoon of milk is optional but recommended. It relaxes the batter a touch and helps achieve a softer, more tender crumb.
• Icing sugar: For the glaze use about 1 2/3 cups of sifted icing sugar. Mixing with warm water yields a glossy, pourable glaze that sets thin and shiny.
• Water for icing: About 7 tablespoons of warm water, added gradually until the glaze reaches a pourable consistency.
• Hundreds and thousands: For decorating, use rainbow sprinkles. Add them immediately after pouring the glaze so they stick while it sets.

Instructions

Preheat and prepare: Preheat your oven to 350°F, or 325°F for a fan assisted oven. Line a 9 by 13 inch baking tin with parchment paper so the traybake releases easily. Proper preheating ensures even rise and an even bake. Cream margarine and sugar: In a large mixing bowl cream together the softened margarine and sugar until light and fluffy. This usually takes 3 to 5 minutes with an electric mixer on medium speed, and it incorporates air which helps the texture. If you are creaming by hand take a little longer to ensure the sugar starts to dissolve into the margarine. Add the eggs: Add the 4 eggs one at a time, beating well after each addition. This helps the eggs emulsify into the fat and prevents the batter from curdling. If the mixture looks slightly separated after an egg, don't worry, keep beating and it will come together. Fold in flour and flavour: Fold the 2 cups of self raising flour into the batter in two or three additions using a spatula, folding gently so you do not overwork the batter. Add the 1 teaspoon of vanilla and the 1 tablespoon of milk, folding until just combined. The batter should be smooth and ribbon slightly when lifted. Bake: Pour the batter into the prepared tin and smooth the top. Bake for 25 to 30 minutes until golden on top and a skewer inserted into the centre comes out clean. Ovens vary so start checking at 20 minutes and use visual cues, the edges should feel set and the centre should spring back lightly. Make the icing: While the traybake cools, sift the icing sugar into a bowl and add warm water one tablespoon at a time until you have a pourable glaze. It should coat the back of a spoon but still pour easily. Glaze and decorate: When the cake is completely cool, pour the icing over the top and use a spatula to spread it evenly. Immediately scatter hundreds and thousands over the glaze while it is wet so they adhere. Leave the icing to set at room temperature for about 30 minutes before slicing into 16 squares.

Storage Tips

Store the traybake at room temperature in an airtight container for up to 5 days. Avoid refrigeration which dries the sponge and mattes the icing. For longer storage freeze slices individually wrapped in cling film and placed in a freezer bag for up to 3 months. To reheat, thaw at room temperature for 30 to 60 minutes and warm gently in a 300°F oven for 5 to 8 minutes if you prefer a freshly baked feel. Keep the icing-covered surface protected to prevent the sprinkles from rubbing off during storage.

Ingredient Substitutions

If you do not have self raising flour, combine 2 cups of plain flour with 3 teaspoons of baking powder. Swap margarine for unsalted butter cup for cup for a richer flavour. If you are dairy free use a dairy free spread labeled for baking. For a gluten free version use a 1 to 1 gluten free flour blend that includes xanthan gum, and you may need to reduce the baking time slightly. You can also use alternative sweeteners but this will change the texture and browning of the sponge.

Serving Suggestions

Serve this traybake on its own for tea, or pair with softly whipped cream and fresh berries for a light pudding. It works well as a base for a simple trifle with custard and fruit. For children's parties serve with decorated slices or stacked mini sandwiches of cake layered with jam. Garnish with extra sprinkles or edible glitter for celebrations.

Cultural Background

This style of sponge is rooted in British school dinner classics, where simple, reliable puddings were made to feed many. The thin icing and sprinkles are a nostalgic touch that became popular mid 20th century when sugar icing and colourful decorations were inexpensive and cheerful. Traybakes like this are practical and communal, designed to be portioned quickly for large groups.

Seasonal Adaptations

In spring add lemon zest to the batter and swap rainbow sprinkles for pastel nonpareils. For winter flavour add a teaspoon of ground cinnamon and top with festive coloured sprinkles. For summer use a light lemon glaze and top with fresh berries just before serving to avoid sogginess. Adjust spice and citrus to complement seasonal fruit.

Meal Prep Tips

To prepare ahead, bake the sponge up to three days before serving and keep it in an airtight container. Ice on the day to preserve brightness of colour and texture. Slice into portions before freezing for easy grab and go snacks. When taking to events, transport in a shallow cake tin with fitted lid to protect the icing and decorations.

This traybake is simple, dependable, and full of comforting memories. Make it your own by adjusting flavours and decorations, and enjoy the ease of a dessert that feeds a crowd with minimal fuss. Share a slice and watch faces light up with nostalgia and joy.