Preheat your oven to 350°F

Line baking sheets with parchment paper and set aside

Add flour, baking soda, and cornstarch in a medium bowl.

Mix to combine.

Set aside.In a large mixing bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy using a hand mixer.

Beat in the eggs, one at a time, followed by the vanilla extract.

Slowly add the flour mixture, stirring until completely mixed and a cookie dough forms.

Gently fold in the M&Ms and sprinkles until evenly distributed throughout the cookie dough.

Transfer cookie dough to the refrigerator. Chill for 30 minutes.

Using a cookie scoop or spoon, drop rounded tablespoons of dough onto the prepared baking sheet, spacing them about 2 inches apart.

Press a few extra M&M candies onto the tops of the  cookies for a more colorful appearance, if desired.

Bake cookies  in the preheated oven for 10-12 minutes, or until the edges are golden brown and the centers are set.

Allow the baked cookies to cool completely on the baking sheets before transferring them to a wire rack. This helps them set and ensures a chewy texture.