Beat together the eggs, flour, caster sugar, butter and baking powder until smooth in a large mixing bowl.
Put the cocoa in separate mixing bowl, and add the water a little at a time to make a stiff paste. Add to the cake mixture.
Turn into the prepared tins, level the top and bake in the preheated oven for about 20-25 mins, or until shrinking away from the sides of the tin and springy to the touch.
Leave to cool in the tin, then turn on to a wire rack to become completely cold before icing.
To make the icing: measure the cream and chocolate into a bowl and carefully melt over a pan of hot water over a low heat, or gently in the microwave for 1 min (600w microwave). Stir until melted, then set aside to cool a little and to thicken up.
To ice the cake: spread the apricot jam on the top of each cake. Spread half of the ganache icing on the top of the jam on one of the cakes, then lay the other cake on top, sandwiching them together.
Use the remaining ganache icing to ice the top of the cake in a swirl pattern. Dust with icing sugar to serve.