Peanut Butter Layer:
1¼ cups creamy peanut butter
1¼ cups butter (2 ½ sticks), cut into 9 pieces
1½ teaspoons vanilla extract
4 cups powdered sugar, sifted
2 cups (entire 12oz pkg) semisweet chocolate chips
1 cup sweetened condensed milk
2½ tablespoons butter
Place peanut butter and butter pieces into a medium microwave safe bowl. Microwave on HIGH for 60 seconds. Stir. Microwave an additional 30 seconds. Stir until smooth. Stir in vanilla extract. Gradually whisk in powdered sugar that has been sifted. Pour into a lightly greased 9 x 13inch pan. Set aside.
In another medium microwave safe bowl, combine chocolate chips, sweetened condensed milk, and 2½ tablespoons butter. Microwave on HIGH for 45 seconds. Stir. Microwave another 30 seconds. Whisk until smooth.
Pour on top of peanut butter layer and use a rubber spatula to smooth it out. Refrigerate for at least 2 hours before cutting into squares. Notes: be sure to buy sweetened condensed milk and not evaporated milk. You will need most of a 14 ounce can. Sifting the powdered sugar will prevent lumps.