01 -
Preheat oven to 350°F. Line 8x8 pan with parchment paper, leaving overhang. Spray bottom with non-stick spray.
02 -
Create double boiler with 2 inches water. Melt butter, chocolate, and sugars together, stirring frequently until glossy but grainy. Remove from heat to cool slightly.
03 -
Whisk in eggs one at a time until mixture becomes lighter and shiny.
04 -
Stir in cocoa powder, salt, and vanilla until combined. Gently fold in flour until just a few streaks remain.
05 -
Pour batter into prepared pan, level top. Sprinkle M&M's over surface.
06 -
Bake 45-50 minutes until edges are set and toothpick 2 inches from edge has few crumbs. Don't overbake for fudgy texture.
07 -
Place pan on wire rack and cool completely before cutting into squares.