Preheat the oven to 180℃/170℃ fan/gas mark 4. Lightly oil and line the base of a 23cm springform cake tin
Place the cocoa powder in a small bowl and slowly add the boiling water, mixing until smooth.
Beat the butter and sugar together until pale and fluffy. Then add the eggs one at a time beating well after each addition, then beat in the vanilla extract.
Add the cocoa powder mixture and mix well, then gently fold in the flour.
Spoon the mixture into the prepared tin and level the top then make a slight dip in the centre. Bake for about 45 minutes until the the cake spring backs when lightly pressed. You can also test with a skewer which should come out clean when inserted into the centre of the cake.
Allow to cool in the tin for 5 minutes, then loosen the edge with blunt knife and turn out onto a wire rack to cool completely. Wash and dry the cake tin and line the edge with baking parchment.
When the cake is completely cold, use a sharp serrated knife to level the top of the cake if necessary and cut into two equal layers. Place one layer back into the tin. Sprinkle with orange liqueur if using.
To make the white and dark chocolate ganache
Melt the white and plain chocolate in separate bowls over a pan of hot water and allow to cool slightly.
Whip the cream until standing in soft peaks, fold half of the cream a little at a time into the white chocolate until just blended.
Next fold the remaining cream a little at a time into the plain chocolate.
Spread half of the white chocolate mixture over the cake in the pan. Then top with the plain chocolate cream and a final layer of white chocolate cream. Top with the remaining cake layer pressing down gently to make sure it comes completely in contact with the cream. Chill for at least 4 hours or overnight.
To complete the cake
Carefully remove the cake from the tin and transfer to a serving plate. Make the chocolate topping, place the butter and chocolate in a bowl and heat over a pan of hot water, stirring until melted and combined.
Allow to cool slightly then spread over the top and sides of the cake with a palette knife. Swirl the icing to give a wavy effect. Decorate with mini white chocolate easter eggs and allow to set.
Alternatively allow the icing to set then pipe rosettes of cream on top of the cake and decorate with berries.
Plan ahead: Allow time for chilling and decorating. Freeze: Undecorated for up to 3 months. Defrost fully before covering with the chocolate icing.Nutrition information is approximate and is meant as a guideline only.