1. Preheat the oven to 180°C, gas mark 4. Grease and line the base of 2 x 18cm cake tins with baking parchment. Using electric beaters, cream the butter and sugar in a bowl for 3 - 4 minutes until fluffy. Beat in the eggs, one at a time, then beat in the vanilla and milk.
2. Gently beat in the flour and cocoa, mixing until smooth. Divide the batter between the tins and bake for 20 minutes, until a skewer inserted into the centre of the cake comes out clean. Leave the cakes in the tins on a rack to cool.
3. For the icing, beat the butter for 2 minutes until creamy, then beat in the sugar for another 2 minutes. Warm the milk in a small pan, then beat into the butter and sugar with the vanilla and cocoa until smooth.
4. Place one of the cakes on a plate and cover with icing. Sit the second cake on top and cover the top and sides with icing. Scatter the chocolate eggs over the cake and serve.