Cut the butter into cubes and add to a bowl with the sugar. Cream together until fluffy and pale.
One at a time add in the eggs, beating in well before adding in the next one. Sieve the flour into the bowl with the baking powder and stir together.
Divide the cake batter into 2/3 and a 1/3 in separate bowls. Add as much of the red food colouring to the larger amount as you wish, depending if you want a red or pink colour.
To the other batter add the cocoa powder and the milk to loosen slightly, then set this aside.
In a greased and lined loaf tin (remember you will be cutting out heart cake out of this so it has to fit the heart cutter you are using) add the red cake batter and place in the hot oven for about 25 minutes, or until completely cooked through.
Once cooled, cut in half. Next, using the heart shaped cutter to cut out two long heart shaped tubes.
Rinse on the loaf tin, grease and line. Place a good layer of the chocolate cake mix in the bottom of the tin, then carefully place the heart cake into the batter, leaving a slight even gap at either end.
Cover with the remaining chocolate cake batter and bake again for about 22 minutes this time, the cake is to be slightly uncool around the heart for a chocolate lava centre around the heart.