Brown the Butter: In a medium saucepan, melt 1 cup of unsalted butter over medium heat, stirring occasionally. Cook for about 5 minutes until the butter turns a rich amber color and develops a nutty aroma. Remove from heat and let cool slightly.

Combine Ingredients: Pour the browned butter into a large mixing bowl. Add in 1 large egg, ¾ cup light brown sugar, ½ cup granulated sugar, and 1 teaspoon of vanilla extract. Whisk until smooth and blended.

Mix Dry Ingredients: Add 2 cups of all-purpose flour, 1 teaspoon of cornstarch, 1 teaspoon of baking soda, and ½ teaspoon of salt. Gently stir until just incorporated.

Add M&M's and Chips: Fold in 1 cup of orange and black M&M’s and 1 cup of semi-sweet chocolate chips into the dough, ensuring even distribution.

Form Dough: Portion out 16 equal mounds of dough on a lined baking sheet. Flatten each mound slightly.

Chill Dough: Cover the baking sheet with plastic wrap or parchment paper and refrigerate for at least 4 hours or up to 5 days.

Preheat Oven: Preheat your oven to 350°F (175°C) about 15 minutes before baking and line additional baking sheets with parchment paper.

Bake Cookies: Place the chilled dough mounds on prepared sheets, spaced about 2 inches apart. Bake for 10.5 to 12.5 minutes until edges are set.

Cool and Serve: Let cookies cool on the baking sheet for about 10 minutes before transferring to a wire rack to cool completely.