To Make the Crepes:
1. Combine all crêpe ingredients in a blender and whiz until completely mixed. Transfer to bowl and let rest for at least 30 minutes or up to overnight in the fridge.
2.Melt a ½ tablespoon or so of butter in a 10-inch non-stick pan over medium heat. Pour a scant ¼ cup of batter into the pan and immediately swirl it around so the entire pan is covered. Cook until the crêpe has browned on the bottom (about 1 minute), then flip with a spatula and finish cooking on the other side for about 30 seconds. Transfer the crêpe to a plate and repeat until you’ve used up all the batter (makes about 20-25 crepes), adding more butter to the pan if necessary. Cool in refrigerator while you make other components.
To Make the Ganache:
1. Heat heavy cream in a medium sized saucepan over medium-low heat until it starts to gently simmer. Remove from heat and pour over chopped chocolate, whisking until chocolate is completely melted and smooth. Add Kahlúa and stir. Let ganache cool completely (you can transfer it to the fridge after it’s cooled down some).
To Make the Cream Filling:
1. Using an electric mixer, whisk cream until soft peaks form. Add sugar, Kahlúa, and cocoa powder and whisk until stiff peaks form. Transfer to fridge until ready to assemble.
To Assemble Cake:
1. Once all components are cold, lay down one crêpe on a plate or cake stand. Spoon a heaping tablespoon of ganache into the center and spread with a spoon or spatula, stopping about ½ an inch from the edges. Top with 1-2 tablespoons of cream filling and spread the same way. Top the filling with the next crêpe, and repeat until you run out of one of the three components (the crêpes will likely go first). Top your last crêpe with a thick layer of ganache.
2. Place crêpe cake in refrigerator until it is firm, then top with a sprinkling of powdered sugar before serving.