Preheat oven to 350°F and prepare a 9×13 pan by lining with parchment paper or coating with cooking spray.
In a large bowl, mix the butter, peanut butter, sugar and brown sugar.
1/4 cup butter, 1 cup peanut butter, 1/2 cup sugar, 1 cup brown sugar
Mix in the eggs and vanilla then the oatmeal and flour until combined.
2 eggs, 1 teaspoon vanilla, 1 1/2 cups quick oats, 2 cups flour
Press 2/3 of the mixture into the bottom of the pan and bake for 10 minutes.
While the bottom layer is baking, make the filling. In a microwave-safe bowl, combine the sweetened condensed milk, peanut butter chips and butter. Microwave on high in 30 second intervals until smooth.
1 14-ounce can sweetened condensed milk, 1 cup peanut butter chips, 2 tablespoons butter
Once the bottom layer is done baking, pour the filling over it and carefully spread it out. Sprinkle chocolate chips on top then place remaining oatmeal mixture on top and press it down lightly.
1 cup semi-sweet chocolate chips
Bake for an additional 20-25 minutes or until the edges are golden brown.