Preheat oven to 350. Line a 9x13 baking pan with parchment.
Cream together the butter and sugar. Add the eggs and mix well. Mix in the sour cream and vanilla.
In a separate bowl whisk together the flour, espresso powder, and baking powder.
Add ⅓ of the dry ingredients to the wet ingredients. Add half the milk. Repeat, until all the ingredients are incorporated.
Spread in the prepared 9x13 pan.
Bake for 15-18 minutes or until a toothpick inserted in the center comes out clean.
Let cool completely. Meanwhile, make the coffee mousse.
Coffee Mousse
Whip the heavy cream until stiff peaks form. Mix in 2 tablespoon of the powdered sugar. Transfer to a separate bowl.
Whip the cream cheese and powdered sugar until light and fluffy. Mix in the instant coffee until completely dissolved and well incorporated. Add ¼ of the whipped cream and mix well.
Slowly fold another ¼ of the whipped cream. The remaining whipped cream will be used during assembly.
Assembly
Cut 2 circles, and two half circles, out of the cake with a 6-inch cake ring. Save the scraps. You will use them.
Line the cake ring with a cake collar.
Put the two half circles into the cake ring. Fill in any gaps with cake scraps.
Pipe coffee mousse around the edge and fill the center with half the whipped cream.
Add the next layer of cake. Pipe mousse around the edge and fill the center with the remaining whipped cream.
Add the top layer of cake. Pipe coffee mousse in florets around the edge. Top each with a chocolate-covered coffee bean.
Chill for at least 3-4 hours, preferably overnight.
To serve: remove the cake ring and then peel away the cake collar.