Brown the butter in a small saucepan. If you're not familiar with browning butter, check out the notes below and in the main post. Let cool slightly so it doesn't cook your eggs when you add those.
1 cup (227 grams) unsalted butter
Preheat your oven to 375°F if baking immediately. Line three cookie sheets with parchment paper or silicone mats. (See notes for suggestions if you do not own three.)
Sift the flour, baking powder, baking soda, and salt into a medium sized bowl.
2 cups (250 grams) all-purpose flour, ½ teaspoon baking powder, ½ teaspoon baking soda, 1 teaspoon salt
Add the sugars to a mixing bowl or the bowl of your stand mixer and mix briefly to combine.
¼ cup (50 grams or 1.8 ounces) granulated sugar, 1 cup (192 grams or 6.8 ounces) dark brown sugar
Beat in the slightly cooled brown butter.
Add the eggs one at a time, then the vanilla, beating about one minute between each addition.
2 eggs, 1 tablespoon vanilla extract
Add the dry ingredients and mix only until just combined.
Add the chocolate chips and M&Ms, reserving a tablespoon or so of each in case your last cookies are light on chips or you want to add extra to the top, and mix by hand.
1 cup (170 grams) chocolate chips, 1 cup (170 grams) M&M candies
Add this point you will need to refrigerate the cookie dough for a few minutes so that you can scoop it, but do not refrigerate it for more than an hour or it will be more challenging to scoop.
Use a #30 cookie scoop or two spoons to scoop two tablespoons of batter onto a baking sheet lined with parchment or silicone mat. If baking immediately, leave at least two inches between cookies. If scooping to freeze, they can be placed adjacent to each other but not touching. Freeze overnight before putting into a freezer bag and squeeze out all of the air.
Bake at 375℉ for 10 to 12 minutes, until the edges are just starting to brown. The centers will still be soft.
Cool on the baking sheet for a few minutes and then move to a cooling rack.