Add both the softened butter and the sugar to the bowl of a stand mixer. Cream it with the whisk attachment over medium speed until fluffy. You can also use a wire whisk.
Add in the egg yolks, continue to whisk to incorporate.
Add in the vanilla concentrate or extract, and three tablespoons of the coffee. Carry on beating for a couple of minutes. Set aside.
Add the whites to a separate bowl. Beat with the whisk attachment over low speed until foamy. Increase the speed to medium, continue to beat until it reaches firm peaks. Fold it delicately into the buttercream.
To assemble the dessert, start by quickly dipping each biscuit into the coffee, then place it on a serving dish in a single layer.
Spread a thin layer of butter cream on top. Repeat the process until you run out of cream. You should finish with a layer of buttercream.
Use a pestle and mortar to crush about 6 biscuits, leaving in some chunks. Sprinkle it on top of the cake.
Pop in the fridge to chill for a couple of hours prior to serving. Enjoy!
