Step 1

Pre-heat the oven to 350 degrees. Butter a 9×13 baking dish.

Step 2

In small saucepan over low heat, melt butter completely. Stir in sugar and continue cooking for 1-2 minutes, stirring constantly. Do not allow sugar mixture to boil.

Step 3

Pour butter mixture into a large bowl or stand mixer. Beat in cocoa powder, eggs, salt, baking powder, espresso powder, and vanilla extract. Mix until well combined.

Step 4

Stir in the flour and M&Ms until well combined. Batter will be thick.

Step 5

Spread into prepared pan and bake for about 30 minutes, until a tester comes out mostly clean about 1-2 inches from the edge of the pan. The edges should be set and the center should still look slightly moist, but not uncooked. Cool on a wire rack.