1. Heat your oven to 350°F (175°C) and line two baking sheets with parchment paper. Set aside.

2. In a medium bowl, combine the flour, baking powder, baking soda, and salt. Whisk well and keep nearby.

3. In a large mixing bowl, cream the butter with both sugars using a hand mixer or stand mixer fitted with a paddle. Beat for about 1–2 minutes, until the mixture looks light and fluffy. Add the cold egg and vanilla, mixing until smooth. Scrape down the sides as needed. Reduce the mixer speed and slowly add the dry ingredients, mixing just until no flour streaks remain.

4. Fold in the M&M’s and white chocolate gently so they don’t break. Pour the sprinkles into a shallow dish and set it next to your workspace.

5. Scoop the dough into portions ranging from 1½ to 2½ tablespoons. Lightly press the top of each dough ball into the sprinkles—don’t flatten them. For thicker cookies, chill the dough balls for about 20 minutes before baking (optional but helpful).

6. Arrange the dough balls on the prepared baking sheets, leaving space between each one. Keep them taller than wide to prevent over-spreading.

7. Bake for 8–11 minutes, until the edges look set but the centers still appear soft. This is the secret to chewy cookies. As soon as they come out, you can gently reshape them if needed (see tips below).

8. Let the cookies cool on the baking sheets placed over wire racks. While still warm, press extra M&M’s or white chocolate on top if desired.