Spray a pan with non stick cooking spray. Melt butter slowly. Add sugar, cocoa and milk. Stir occasionally while the mixture comes to a boil. Once the mixture comes to a boil, stir and boil the mixture for 3 minutes. Remove from heat. Add vanilla extract and stir mixture. Quickly add the oatmeal (and nuts if using) and stir. (If using the butter substitute, increase dry oatmeal to 3-1/2 cups to help thicken the mixture.) Drop by spoon onto greased cookie sheet or waxed paper and allow to cool uncovered. Refrigerate cookies after 5 minutes.