In a saucepan over medium heat, melt butter. Swirl it until brown in color and it reaches a nutty aroma. Remove from heat.
1 cup unsalted butter
Meanwhile, in a large stand mixer fitted with the whisk attachment or mixing bowl, combine sugar, brown sugar, and vanilla. Pour browned butter in and whisk to combine.
¾ cup white granulated sugar, 1 cup light brown sugar, 1 tablespoon vanilla extract
On low speed, add eggs, one at a time until just incorporated.
2 large eggs
Add baking soda, baking powder, salt and flour to mixture and fold in until combined.
1 teaspoon baking soda, ½ teaspoon baking powder, ¼ teaspoon salt, 3 cup all-purpose flour
Fold in M&M's and chocolate chips. (If you want to prevent marbling, allow mixture to cool before folding in.)
1 cup M&M's, ½ cup chocolate chips
Place large dough balls onto parchment lined cookie sheet and refrigerate 30+ minutes. Optional: Press M&M's on top and freeze for 4+ hours for big, thick cookies.
Preheat oven to 350°F. Optional: top cookies with thick flakes of sea salt. Bake 12 minutes or until edges are golden.