In a bowl, whisk the softened butter for 5 minutes. Add the sugar and whisk for 5 more minutes. Then add the 3 yolks, and whisk 5 minutes again.
Add the teaspoon of sugar into the coffee. Quickly dip a biscuit in it, no more than 5 secondes or your biscuit will be too damp.
Arrange the dipped biscuits on a plate forming a flower.
Spread a thin layer of buttercream .
Repeat step 3 and 4 until you only have 5 biscuits left.
Spread a thicker layer of buttercream on the top of the cake. Then, sprinkle with the crushed biscuits you had left.
Put in the fridge for a few hours, then there you are ! Enjoy !