1Sift together confectioners' sugar, cocoa and salt. Set aside.
2In a double boiler over medium heat melt the unsalted butter. Add sugar-cocoa mixture. It will be very thick. Begin adding evaporated milk a little at a time and keep stirring. Keep adding milk until it has a smooth silky texture. Remove from heat. Add peanut butter and vanilla extract, mixing well. Pour into a 8" or 9" square pan which has been sprayed with non-stick cooking spray.
3Cool completely. Take a pizza cutter and cut into small squares. Store in refrigerator in airtight container.