Preheat your oven to 350°F (175°C).
In a large mixing bowl, whisk together the melted butter, light brown sugar, and creamy peanut butter until smooth. Add in the egg and vanilla extract, mixing until fully combined.
In another bowl, whisk together the all-purpose flour and a pinch of salt. Gradually add the dry ingredients to the wet mixture, stirring until just combined.
Gently fold in the mini peanut butter cups and Peanut Butter M&Ms, ensuring they are evenly distributed throughout the batter.
Spoon the cookie batter into a greased 9-inch pie dish, spreading it out evenly with a spatula.
Place the pie in the preheated oven and bake for 25-30 minutes, or until the edges are golden brown and the center is set.
Allow the pie to cool in the dish for about 10-15 minutes before slicing and serving.
