Preheating your oven to 190°C / 374°F Gas mark 5.
Grease two 20cm / 8” sandwich cake tins and line the bottoms with greaseproof paper.
Add the butter and caster sugar to a bowl and cream together using a spatula to a smooth paste.

Whisk in the eggs 1 at a time (make sure your eggs are at room temperature).
Add the vanilla extract and concentrated coffee solution and mix in.
Sift in the flour and baking powder and gently fold it into a smooth batter using a spatula.
Divide the batter equally into the 2 prepared sandwich cake tins, levelling off the batter, and get them into the preheated oven and set your timer for 20 minutes.

While the sponges are baking, start the coffee flavoured cream, by adding the double, heavy, or whipping cream, coffee solution, vanilla extract, and icing sugar to a bowl, and whisk until thick. cover and refrigerate until needed.
When the time is up on the sponge cakes, (do not open the oven door before) check the cakes using a cocktail stick or wooden skewer, if it comes out clean the cake is done, if not! give them a couple of more minutes.

Place one of the cakes on a serving plate with the bottom of the sponge facing up, cover with half of the coffee cream, staying shy of the edge, and level it off, gently line up and place the second cake on top of the cream with the flat bottom of the sponge facing down this time, gently press it down.
Cover the top of the cake with the remaining cream, and decorate with the walnuts.
Slice and serve.