Preheat oven to 350 degrees F. Line a large baking sheet with a Silpat baking mat or parchment paper and set aside.

In a large bowl, whisk flour, cornstarch, baking soda and sea salt together. Set aside.

In the bowl of a stand mixer, cream together butter and sugars until smooth and creamy, about 3 minutes. Add egg and vanilla extract and beat until combined. Slowly mix in the dry ingredients.

Stir in the M&M'S MINIS® and mini chocolate chips. Form cookie dough into teaspoon balls and place on prepared baking sheet, about 1 inch apart.

Bake cookies for 8 minutes, or until slightly golden brown around the edges. Let the cookies cool on the baking sheet for two minutes. Transfer to a wire cooling rack and cool completely.