Preheat oven to 350°F and line an 8×8 baking dish with parchment paper.
Brown the butter in a light-colored saucepan over medium-low heat. Once melted, simmer for 3-5 minutes until it turns brown with a nutty aroma.
In an electric mixer, combine brown butter and coconut sugar. Mix for 1-2 minutes on medium speed.
Add eggs and vanilla extract, then whisk until fully combined.
Switch to a paddle attachment and add flour, baking soda, and salt. Mix until just combined.
Fold in M&M’s and chocolate chips until fully incorporated.
Press dough into the prepared pan and top with more holiday M&M’s. Bake for 17 minutes, then gently smack the pan on the counter to remove air bubbles.
Return to the oven and bake for an additional 8-10 minutes.
Let cool for 30 minutes, then slice into 12 squares and enjoy!