Start by greasing and lining a large loaf cake tin. To make the coffee cake, dissolve the coffee granules in the hot water and put aside to cool. Make the cake as a Victoria sponge by beating together the butter and sugar till light, then add the eggs one at a time, then sift in the flour and baking powder and fold in. Finally, fold in the orange zest, dissolved coffee granules and walnuts. Put the cake mixture into the prepared cake tin and level out. Bake in the oven at 200`c for about 45 minutes, or until the cake springs back when pressed. Remove the cake from the oven and leave to cool on a wire rack. Next, while the cakes cool down, you can prepare the coffee cream filling. Put the remaining coffee granules and coffee liqueur into a saucepan and heat gently to dissolve the coffee granules. Leave to cool completely. Next, place the butter in a bowl and beat till light and fluffy. Slowly stir in the icing sugar, and then add in the dissolved coffee and liqueur and continue mixing till you a have a smooth cream filling. Cut the loaf cake in 3 horizontally. Use 2/3 of the coffee cream filling to sandwich the 3 layers together. Place the cake onto a long serving plate and spread the remaining coffee cream on the top. Finally, decorate the top of the coffee cake with walnut halves and chill for an hour before serving.