Preheat the oven to 160C. Lightly grease two 20cm/8in loose-bottom sandwich tins and line the bases with parchment paper.
In a second bowl, beat the butter and sugar until light and fluffy. Add the eggs, sprinkle the flour and baking powder and coffee essence and beat until well combined and smooth.
Divide the mixture evenly between the tins. Level the surface using a spatula or the back of a spoon.
Bake for 30-35 minutes, or until baked fully. Remove from the oven and set aside to cool. Leave the cakes to cool in the tins for 5 minutes, then carefully turn the cakes out onto a wire rack. Peel off the paper and leave to cool completely.
Next, prepare the butter icing. In a large bowl, combine the butter with the icing sugar, coffee essence or cooled espresso. Beat the mixture until smooth and fully combined. Place in a piping bag.
When the cakes have cooled down, place the base layer on a serving plate. Spread with some apricot jam then some buttercream if desired. Add the second cake and pipe the remaining buttercream.
Decorate with the walnuts and drizzle over the caramel sauce. Set aside to cool for 20 minutes.
Serve within 2-3 days.
