Preheat the oven to 180°C/160°C fan oven/Gas Mark 4. Grease and line 2 x 8” round cake tins. Pop the coffee granules in a jug and add the boiling water, stir until the coffee granules have dissolved and leave to one side.

Place the margarine and sugar into a bowl and cream together until smooth. Add the eggs and beat into the creamed mixture, if the mixture begins to curdle add a spoonful of flour. 

Gently sieve the flour, Baking Powder and xanthan gum on top of the mixture and fold in and finally fold in the coffee and chopped walnuts.

Divide the mixture between the prepared cake tins and bake in the oven for 35-40 minutes until risen and skewer inserted into the centre comes out clean. Leave the cakes to cool in the tins for 15 minutes, then remove and place on a wire rack to cool completely.

Whilst the sponges are baking make the caramelised walnuts, line a baking tray with non-stick baking parchment. Put the caster sugar in a non-stick frying pan and heat over a gentle heat until it has melted. There is no need to stir, but the occasional swirl of the pan will help mix everything evenly. 

Once all the sugar has melted and you have a clear, golden caramel, add the walnuts to the pan and swirl to coat them in the caramel. Quickly tip the caramel onto the lined baking tray in an even layer and leave to cool and set at room temperature.

Whilst the cakes are cooling make the buttercream. Place the coffee granules into a jug and add the boiling water, stir until the coffee granules have dissolved and place to one side.

Place the butter in a bowl and beat until glossy. Add half the icing sugar beat into the butter, once incorporated add the remaining icing sugar and continue to mix the buttercream. Add the coffee mixture and beat the buttercream until light and fluffy in texture.

Once cooled flatten the top of one of the cakes, using a serrated knife. Place half the buttercream into the sponge you have flattened and spread to evenly cover the sponge. Sandwich the other layer of sponge on top with the domed side facing up. Spread the remaining buttercream on top of the cake.

Pop the Chocolate and cream into a bowl. Melt in the microwave for 30 seconds and stir, if it is not fully melted heat in 10 seconds bursts stirring between each burst until you have a lovely smooth ganache. 

Drizzle your ganache over the top of the cake using a spoon. Break your cooled caramelised walnuts into pieces and pop onto the top of your cake. 

You are now ready to serve your gluten free coffee and walnut cake!