Preheat oven to 350 degrees. Grease and line four 9-inch pans with parchment rounds and set aside. (This recipe only uses three of the four cakes, so you will have some left over!)
Use a double boiler to melt together the butter, pound of the chocolate chips, and unsweetened chocolate until smooth. Cool to room temperature. (If you want, save some to re-melt at the end for decoration.)
Combine the eggs, powdered espresso, vanilla, and sugar; stir in the cooled chocolate and set aside for later.
Sift together the dry ingredients, then mix into the chocolate batter. Fold the remaining chips and nuts into the batter. Divide evenly into greased pans.
Bake about 30 minutes, or until toothpick inserted in center comes comes out clean. (They will be slightly fudge-like.) Let cool, then turn upside down and remove parchment.
Set up the cake ring (or parchment paper ringing the mold) with a card board round on the bottom and the acetate along the inside of the ring. Place one round of the cooled brownie on the bottom and spoon in the 1st ice cream flavor.
To ensure a pretty end result, make sure to smooth the ice cream to the very edges and press down. Place in freezer for 15 mins if the ice cream has really softened.
Repeat this process with another brownie layer and another ice cream flavor. (I like three layers of each.) End with a smooth layer of ice cream that is flat enough for decorating.
After decorating, freeze for several hours before serving.