1. In the top half of a double boiler, melt 3 cups of semi-sweet chocolate chips, 1 cup white chocolate chips and 1/4 cup butter until soft enough to stir.
2. Stir in the confectioner’s sugar and Irish cream until mixture is smooth. Stir in walnuts.
3. Pour mixture into a buttered 8x8” baking pan and with a sheet of plastic wrap touching the mixture, press and smooth out the surface.
4. In the top half of a double boiler melt remaining chocolates until soft. Remove from heat and with a fork beat in the butter and Irish cream until smooth. Spread topping over cooled fudge with a knife. If a smooth top is important place plastic wrap over the top. Refrigerate until firm, 1 to 2 hours at least. This fudge can be easily frozen.