Preheat the Oven: Preheat the oven to 350°F. Line two baking sheets with parchment paper and set aside.
Mix Dry Ingredients: In a medium bowl, whisk together the flour, cornstarch, baking soda, and salt. Set aside.
2 ½ cups all-purpose flour, 2 teaspoons cornstarch, 1 teaspoon baking soda, ½ teaspoon salt
Cream Butter and Sugars: In a large mixing bowl, beat the butter, brown sugar, and granulated sugar until creamy and fluffy, about 1 minute.
14 tablespoons unsalted butter, 1 cup light brown sugar, ½ cup granulated sugar
Add Egg and Vanilla: Mix in the egg and vanilla extract until fully combined.
1 large egg, 3 teaspoons vanilla extract
Combine Wet and Dry Ingredients: Gradually add the dry ingredients to the wet mixture, stirring until just combined.
Fold in Chocolate and M&Ms: Use a wooden spoon or spatula to gently fold in the chocolate chips and M&Ms.
1 ¼ cups semi-sweet chocolate chips, 1 cup Easter M&Ms
Form Dough Balls: Scoop out heaping spoonfuls of dough and roll into balls. Press a few extra M&Ms and chocolate chips on top of each cookie for a bakery-style look.
Chill the Dough (Optional but Recommended): For the best texture, cover and refrigerate the dough balls for 30 minutes. If chilling overnight, let them sit at room temperature for 15-20 minutes before baking.
Bake the Cookies: Place the dough balls on the lined baking sheets, spacing them about 2 inches apart. Bake for 8-10 minutes, until the edges are slightly golden but the centers look slightly underbaked.
Cool the Cookies: Let the cookies rest on the baking sheet for 5 minutes, then transfer them to a wire rack to cool completely. The cookies will continue to firm up as they cool.
Enjoy: Serve warm or store in an airtight container for up to 5 days. These cookies also freeze well for up to 3 months!