Vanilla Sheet Cake

From Edd Kimber - One Tin Bakes

The Cake
400g plain flour
1 ¼ teaspoons baking powder
2 ½ teaspoons bicarbonate of soda
1 teaspoon salt
400g caster sugar
3 large eggs
135 ml neutral oil - I used plain vegetable (rape seed) oil
285 ml buttermilk
1 tablespoon vanilla extract
240 ml boiling water

The Frosting
240g unsalted butter, diced and at room temperature
2 large egg whites
1/8 teaspoon cream of tartar
Pinch of salt
150g caster sugar
Seeds from 1 vanilla pod

9 x 13 inch brownie tin

Preheat the oven to 180 deg C, gas mark 4. Lightly grease the baking tin and line with parchment so that the paper overhangs the two long sides.

For the cake; add the flour, baking powder, bicarbonate of soda, salt and sugar into a large bowl and whisk to combine. Make a well in the middle and add the eggs, oil, buttermilk and vanilla, then whisk until you have a smooth, well combined, batter. Pour in the boiling water and whisk briefly to mix. The batter will be very thin.

Pour the batter into the prepared tin and bake for 35 - 40 minutes, until a skewer inserted into the middle comes out clean.

Leave the cake to cool in the tin for 20 minutes and then remove using the overhanging baking parchment to lift it out. Leave to cool completely on a wire rack.

Whilst the cake is cooling, make the frosting. Place the egg whites, cream of tartar, sugar and vanilla seeds into a large heatproof bowl. Place the bowl over a pan of simmering water, making sure the bottom of the bowl does not touch the surface of the water. Stir regularly until the sugar has dissolved and the mixture is hot to the touch.

Remove the bowl from the heat and, using an electric mixer, whisk for about 7 - 10 minutes until the meringue has cooled to room temperature. Still whisking, slowly add the butter, a piece or two at a time. Mix until you have a buttercream like, silky smooth texture.

Spread the buttercream over the cooled cake and top with sprinkles of your choice.