Preheat the oven 170°/ 325°F/ GM3
Grease and line 3 x 6-inch circular baking tins (note these are smaller than average tins - if you are using 8-inch tins see my notes on how to scale up the recipe)
Melt the 3 types of chocolate in separate bowls. Set aside
In a bowl beat the butter and sugar until light and fluffy, using electric beaters. Add the eggs, one at a time, beating well between each addition
Add 3 tablespoon of milk and beat again. Sift the flour and baking powder into the bowl and mix well
Divide the cake batter equally into 3 small mixing bowls
For the White Chocolate & Vanilla Sponge: from the first mixing bowl take a tablespoon of the cake batter and stir it quickly into the melted white chocolate. Then gently fold this white chocolate mixture and the vanilla extract back into the bowl containing the rest of the cake batter. This double-action will stop the chocolate from seizing when it is mixed into the cake batter. Gently spoon the batter into one of the baking tins and spread it out with a blunt knife
For the Malted Milk Chocolate Sponge: stir an extra tablespoon of milk and the Ovaltine powder into the second bowl of cake batter. From this bowl, take a tablespoon of the cake batter and stir it quickly into the melted milk chocolate. Then fold this chocolate mixture back into the rest of the cake batter. Spoon the batter into another of the baking tins & spread it out
For the Dark Chocolate Sponge: stir an extra tablespoon of milk and the cocoa powder (sifted) into the remaining bowl of cake batter. Quickly mix a tablespoon of this cake batter into the melted dark chocolate, then fold this chocolate mixture back into the rest of the cake batter. Spread the batter into the last of the baking tins
Bake all three cakes for 20-25 minutes until the cake springs back when lightly pressed or a skewer comes out clean
Let cool in the tins for 2 minutes, then remove from the tins, peal off the baking parchment from the bottom of each sponge cake and let cool completely on a wire rack