- Preheat the oven to 180°C/Gas 4. Lightly grease the cake pans.
- Place the butter, sugar, flour and eggs in a bowl. Mix until well combined using an electric hand mixer.
- Divide the mixture evenly into 5 bowls then add your chosen colours using a cocktail stick ─ as only very small amounts are required, take care to add just a little at a time then keep adding a little more until you reach your desired shade.
- Transfer the mixtures into the pans, spreading them evenly then make a slight dip in the centre of each to help to achieve an even rise.
- Place all the pans in the oven, evenly spaced, and bake for 18 minutes until a skewer inserted into the middle of each cake comes out clean. Set aside and cool for 5 minutes, then remove from the pans and transfer to a wire rack and cool completely.
- To assemble the cake, smear a small amount of frosting on a cake stand or plate to secure the first sponge. Spread a layer of frosting to the edges of this sponge then top with the next colour sponge. Repeat with the remaining sponges.
- Spread the remaining icing thickly and smoothly all over the sides and top of the cake and then draw a palette knife around the sides to create ridged rings. Place the chocolate eggs in the centre on top of the cake.