Preheat oven to 350 degrees. Line an 8x8 inch pan with parchment paper and lightly grease paper.
Sift together flour, baking powder, baking soda, and salt; set aside.
Melt butter on the stove or microwave, once melted mix with brown sugar.
Mix together egg, vanilla, and brown sugar mixture.
Slowly add flour mixture, mix until well combined.
Stir in M&M's then press batter into pan.
Bake for 20-25 minutes.
Cool and enjoy!