Melt butter and crush Ritz crackers. Mix together and spread in 9 x 13 inch pan. Bake 10 minutes at 300 degrees. Mix pistachio pudding with milk until thick. Add ice cream and spread over cooled crumbs. Freeze. When solid, spread Cool Whip on top. Crush candy bars in plastic bag and spread over Cool Whip. Freeze. Thaw 10 minutes before serving.
Chocolate pudding can be substituted for pistachio.