In a large mixing bowl, cream together butter and sugars.
Add peanut butter and mix well.
Add eggs, one at a time, until incorporated.
Combine flour, salt, baking powder, and baking soda and add gradually to peanut butter mixture, mixing until all ingredients are well-blended.
Using 1/3 c. dough at a time, roll into balls and dip in sugar to coat.
Place on a lightly greased cookie sheet and use a glass to flatten cookies just until edges start to crack (you will flatten them more later).
Bake at 350 degrees for 15 minutes.
Open oven and use a glass to flatten cookies to desired size.
Bake for an additional 5-7 minutes or until edges are golden brown.
Cool completely.
Top cooled cookies with 1 Tbsp. peanut butter, 1 crumbled peanut butter cup, and 8-10 m&m's.
Prepare chocolate ganache by heating heavy cream until boiling, then pouring over chocolate chips in a heat-proof bowl.
Stir mixture until smooth. *If necessary, heat additionally to completely melt chocolate chips.
Drizzle chocolate over cookies and refrigerate until set.