Step 1Put the instant coffee into one of the mixing bowls. Measure out 150 ml of boiling water from the kettle into a measuring jug. Add to the coffee and stir until dissolved. Add the booze and set aside to cool slightly.
Step 2Tip the double cream into another mixing bowl. Add the icing sugar and whisk by hand until the cream just holds its shape – don’t overdo it, you want it to be pillow-y and light.
Step 3One by one, dunk half of the sponge fingers into the booze and coffee liquid, for 5-10 seconds at a time (just enough so they soak up some coffee, but not too long so they disintegrate) and lay in the baking dish. Spread over half of the whipped cream with a spatula. Repeat the dipping and layering process with the other half of the sponge fingers and cream, making sure the sponge fingers soak up all the coffee goodness. Pour any extra boozy coffee on top.
Step 4Sift over some cocoa powder to finish, then dig in.
Cook's tip: Get everything laid out in a production line so that you can dunk the sponge fingers, lay them straight in the dish and then cover in the cream. Having only two layers also helps speed things up.