Preheat the oven to 160C. Lightly grease two loose-bottomed 20cm/8in 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 20–30 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. Cover with cling film and keep aside until needed.
When the cakes have cooled down, place the base layer on a serving plate. Spread with some apricot jam then half the buttercream. Add the second cake and spread the remaining buttercream.
Decorate with the walnuts and pecan and drizzle over the chocolate sauce. Set aside to cool for 20 minutes.
Serve within 2-3 days.