Get Ready to Bake: Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper for easy cleanup.
Dry Mix Magic: In a medium bowl, whisk together your flour, baking powder, baking soda, and salt until well combined. Set this aside.
Creamy Goodness: In a larger bowl, using an electric mixer, beat the softened butter with both granulated and brown sugars for 1-2 minutes until it's wonderfully light and fluffy.
Wet Ingredients In: Mix in the egg and vanilla extract until everything is just combined. Remember to scrape down the sides of the bowl!
Combine and Conquer: Slowly add the dry flour mixture to the wet ingredients, mixing on low speed until the dough just comes together. Don't overmix!
Add the Fun Stuff: Gently fold in about 1 cup of your M&M's (or M&M's and chocolate chips) into the cookie dough.
Shape & Decorate: Pour the sprinkles into a shallow bowl. Scoop out 1 ½ to 2 ½ tablespoon portions of dough. Lightly press a few extra M&M's onto the top of each dough ball, then gently press the top of the ball into the sprinkles. This gives them that festive look!
Bake Away: Place your decorated cookie dough balls onto the prepared baking sheets, leaving a couple of inches between each. Bake for 8-11 minutes. You want the edges to look set, but the centers should still be a little soft for that perfect chewy texture.
Cool Down: Let the cookies cool on the baking sheets for a few minutes before transferring them to a wire rack to cool completely. They'll firm up as they cool, ready for enjoyment!