In a saucepan, heat the butter and sugar over medium heat, whisking until the sugar dissolves. Cook until it’s bubbling and let it boil for 2 minutes. Remove from the heat and stir in the oats until completely moistened. Set aside.
Place the chocolate chips and peanut butter in a bowl. Melt in the microwave (30 seconds at 50% power, stirring after each time) or a double boiler until the chocolate chips are melted.
Press half of the oat mixture into the baking dish. Pour the melted chocolate over top, spreading with a spatula. Gently press the remaining oat mixture over top. Let cool completely or refrigerate (I love these cold!) – let sit for a few hours (3 to 3) before slicing.