Preheat oven to 350 degrees F.
Line baking sheet with parchment paper or silicone liners.
Mix together butter, peanut butter, and sugars.
Add egg, vanilla extract, and milk. Mix well.
Stir in Cassava and oat flours, baking powder, baking soda, and optional salt.
Add the chips, nuts, and candy (except the peanut butter M&Ms) and stir well.
Drop 2 tbsp of dough for each cookie on the prepared cookie sheet, leaving some space between, as they will spread while baking. Place a peanut butter M&M on top of each cookie and gently flatten to half the size.
Bake for 9-10 minutes. Remove from oven and let rest before transferring cookies to a cooling rack.
Freeze for longer storage.