01 -
Preheat the oven to 350°F and line a baking sheet with parchment paper.
02 -
Using a mixer, cream together softened butter, smooth peanut butter, brown sugar, and granulated sugar until light and fluffy.
03 -
Add the egg and vanilla extract to the creamed mixture and blend until smooth and fully combined.
04 -
In a separate bowl, whisk together all-purpose flour, baking powder, baking soda, cornstarch, and salt. Gradually add the dry mix to the wet mixture, stirring until no streaks of flour remain.
05 -
Scoop nine equal portions of dough using a large cookie scoop. Roll each into a ball, flatten to approximately 1/4 inch thickness, then freeze the discs for 15 minutes to firm.
06 -
Bake the chilled dough discs in the preheated oven for 12 to 13 minutes until edges are set and centers slightly soft.
07 -
Combine milk chocolate chips and vegetable oil in a microwave-safe bowl. Heat in 30-second intervals, stirring between each, until smooth and fully melted.
08 -
Immediately spread the melted chocolate over each warm cookie, then sprinkle with muddy buddies pieces. Allow to cool completely on the baking sheet before serving.