Melt butter in a saucepan over medium heat until golden brown and nutty. Let cool.
Whisk together flour, baking powder, and salt in a medium bowl.
Beat together brown sugar, granulated sugar, eggs, and cooled brown butter in a large bowl. Stir in vanilla extract. Gradually add dry ingredients to wet ingredients, mixing until just combined.
Fold in M&Ms
Grease an 8x10-inch baking pan. Pour the dough into the pan and spread evenly. Bake for 25-30 minutes or until a toothpick inserted into the center comes out clean.*
Allow the bars to cool for at least half an hour before cutting into squares.
Notes
Don’t overbake! You want a toothpick inserted into the center to come out ‘mostly’ clean. A few crumbs on it is ok!
Check your bars at 25 minutes. If you notice them browning to much, loosely tent with foil.
You can line your baking dish with parchment for easier removal!
Leave the bars in the dish for at least half an hour before cutting them or trying to remove them.