Melt butter in a medium saucepan. Remove from heat and add milk and vanilla.

Sift sugar, cocoa and salt together.

Gradually add sugar mixture to milk mixture stirring until blended.

Stir in peanut butter. I try to leave a few streaks of peanut butter showing but you can stir it completely in if you want.

Press mixture into buttered 8-inch square pan. I line my pan with parchment for easy removal.

Cover and chill. Cut into squares. Keep refrigerated.