Preheat the oven to 170°C and grease three 23x33cm baking trays with parchment.
Grind walnuts and sugar in a food processor to a coarse powder consistency.
Cream butter into the walnut mixture, then sift in flour, coffee, and all remaining sponge ingredients.
Spread the mixture into trays and bake for 10-12 minutes until golden and springy.
Cool the cakes briefly before transferring them to wire racks for total cooling.
Cut out 54 circles from the cooled sponges using a 5cm round cutter.
Mix 350g icing sugar, butter, half the coffee paste, and lustre dust into a smooth buttercream.
Combine the remaining coffee paste, water, and 150g icing sugar to create a liquid glacé icing.
Stack three cake circles with layers of buttercream between them.
Drizzle glacé icing over stacks and decorate with crushed walnuts and chocolate coffee beans.