Ingredients

• 250g/9oz unsalted butter
• softened
• 250g/9oz caster sugar
• 250g/9oz free-range eggs
• weighed in their shells (about 4 medium eggs)
• 250g/9oz self-raising flour
• sieved
• 3 medium free-range egg whites
• 250g/9oz caster sugar
• pinch salt
• 300g/10½oz unsalted butter
• softened and cubed
• 3 tbsp strawberry milkshake powder
• 75g/2½oz rainbow-coloured sprinkles
• 3 strawberry-filled sandwich biscuits
• cut in half

Directions

• Preheat the oven to 190C/170C Fan/Gas 5. Grease and line a 14x20cm/5½x8in cake tin or 900g/2lb loaf tin.
• For the cake
• put the butter
• sugar
• eggs and flour into a large mixing bowl. Using an electric hand whisk
• beat for 3 minutes on medium speed until smooth and shiny.
• Spoon the batter into the prepared tin. Level off the top
• then bake on the middle shelf for 45–50 minutes
• or until a skewer inserted comes out clean and the cake is golden-brown and well risen. Leave to cool for 10 minutes in the tin
• then turn out to cool completely on a wire rack.
• Meanwhile
• for the strawberry Swiss meringue buttercream
• put the egg whites
• sugar and salt into a heatproof bowl. Place over a pan of gently simmering water (do not let the bottom of the bowl touch the water).
• Using an electric hand whisk
• mix on high speed for 5 minutes
• or until glossy and thick. Remove from the heat and beat for 2 minutes
• or until cooled to room temperature.
• Now quickly add the butter a cube at a time until you have used up all of it. The mixture may look quite loose and split
• but don’t be alarmed – keep beating until it has cooled
• thickened and come together. Beat in the strawberry milkshake powder until well incorporated.
• Once the cake has cooled completely
• trim the top and sides if necessary so the rectangle is neat and flat. Turn the cake upside down onto a cake board or stand.
• Put half the buttercream in a piping bag with a large round tip nozzle attached and set aside. With the remaining buttercream cover the sides of the cake using an offset spatula.
• Pipe tall peaks around the top edge of the cake. Scatter the sprinkles over the centre. Decorate the tops of some of the icing peaks with halved sandwich biscuits .