Note: This dough requires chilling.

Cream butter and brown sugar in the bowl of a stand mixer fitted with the paddle attachment. Mix in egg and vanilla until smooth. Add pudding mix, baking soda, and salt. Mix until combined. Mix in flour, then stir in sprinkles and M&Ms.

Scoop 2 tablespoon balls of cookie dough onto a cookie sheet covered with parchment or a silpat baking mat. Chill for at least 30 minutes.

Preheat oven to 350°F. Line cookie sheets with parchment paper or silpat baking mats. Place chilled cookie dough balls 2 inches apart. Bake 9-11 minutes until edges turn brown. Cool on a rack. Store in an airtight container for up to 4 days or freeze for up to one month.