Prepare the Oven and Baking Sheet:
Preheat your oven to 350°F (180°C) or 160°C if using a fan oven. Line a baking sheet with parchment paper or a Silpat silicone baking mat. Set it aside.

Mix the Dry Ingredients:
In a medium mixing bowl, combine the all-purpose flour, baking soda, baking powder, and salt. Set this dry mixture aside.

Cream the Wet Ingredients:
In a separate large mixing bowl, use a hand mixer to cream the softened butter, granulated sugar, and light brown sugar together until light and fluffy.

Add Egg and Vanilla:
Beat in the egg and vanilla extract until fully incorporated.

Combine Wet and Dry Ingredients:
Gradually add the dry mixture to the wet mixture, a little at a time, mixing thoroughly after each addition. If the dough becomes too thick, finish mixing by hand with a spatula.

Fold in Add-ins:
Gently fold in the Holiday M&M’s, chocolate chips, crushed pretzels, and sprinkles until evenly distributed throughout the dough.

Shape the Cookies:
Use a medium cookie scoop to drop dough balls onto the prepared baking sheet, leaving about 2 inches of space between each cookie.

Bake the Cookies:
Bake in the preheated oven for 9-11 minutes, or until the edges of the cookies are lightly golden brown.

Cool the Cookies:
Let the cookies cool on the baking sheet for 2 minutes before transferring them to a wire rack to cool completely.