Preheat oven to 350°F. Line two baking sheets with parchment paper.

In a bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.

In a separate bowl, using a hand mixer or stand mixer fitted with the paddle attachment, beat butter and both sugars for 1-2 minutes, until light and fluffy. Add egg and vanilla extract, mixing until combined, scraping the sides of the bowl as needed. On low speed, add in flour mixture and mix until just combined.

Gently stir in M&M's and white chocolate chips. Place the sprinkles in a shallow bowl.

Scoop balls of cookie dough, between 1 1/2 and 2 1/2 tablespoon portions. Gently press the top of each ball into the bowl of sprinkles. You can bake the cookies right away or chill the dough balls in the fridge for about 20 minutes for slightly thicker cookies.

Place dough onto prepared baking sheets leaving an inch or two for spreading. Make sure the dough balls are mounded higher rather than wider so the cookies aren't too thin.

Bake for 8-11 minutes, until the edges of the cookies are set but the center is still slightly underdone; this will create a soft cookie.

Place the baking sheets on wire racks and allow the cookies to cool completely. If desired, press some M&M's and/or chocolate chips onto the top of the cookies when they are still warm.