Preheat the oven to 350 degrees and line a 9x13 dish with parchment or spray with nonstick spray.

In a large bowl, combine the oats, flour, baking soda, and salt.

In the bowl of your stand mixer, cream together the butter, peanut butter, and sugar until light and creamy.

Beat in the eggs one at a time. Stir in the vanilla until combined.

Stir in the Reese's Pieces and chocolate chips until distributed throughout the cookie dough.

Combine the wet and dry ingredients and mix until combined.

Press 2/3 of the cookie dough into the prepared pan.

Add the condensed milk, semisweet chocolate chips, peanut butter, butter, and salt to a small saucepan over low heat and heat, stirring often, until the mixture is smooth.

Spread the chocolate mixture over the cookie dough.

Take small chunks of the remaining cookie dough and flatten them with your hands and drop them over the chocolate mixture in a single layer. The top layer will not cover the chocolate completely. There should be some gaps.

Bake for 25-30 minutes or until golden brown. Cool completely before cutting.