01 -
In a large mixing bowl, whisk together the all-purpose flour, baking soda, cornstarch, and salt until uniformly blended.
02 -
In a separate bowl, whisk the melted butter, light brown sugar, and granulated sugar until the mixture is smooth and combined. Add the egg, additional egg yolk, and vanilla extract, then whisk until fully integrated.
03 -
Gradually stir the wet mixture into the dry ingredients, mixing until a soft dough forms with no visible streaks of flour.
04 -
Using a spatula, gently fold in the semi-sweet chocolate chips and Christmas M&Ms until evenly distributed throughout the dough.
05 -
Cover the dough and refrigerate for at least 30 minutes to allow the flavors to meld and prevent overspreading.
06 -
Preheat oven to 350°F. Line baking sheets with parchment paper. Scoop balls of dough, about 2 tablespoons each, and arrange them evenly on the prepared sheets.
07 -
Bake in the preheated oven for 10-12 minutes, or until edges are lightly golden while centers remain soft. Remove from the oven and allow cookies to cool on the baking sheets for 5 minutes before transferring to a wire rack.