In a buttered pan, combine sugar, cocoa, and milk cooking until the sugar dissolves. The butter on the pan eliminates sugar crystal build up. Boil, and bring to a soft ball stage. Remove from heat, add butter, vanilla, beat until smooth, stir in peanut butter &/or nuts.
Pour onto a buttered cookie sheet or 11x7 casserole. Let set until firm. If for some reason it doesn't get hard, then you didn't cook it enough.
I have made these for Christmas and parties. Don't try to make 2 batches at the same time, unless you are better at multi-tasking than I am.