Line air fryer tray or basket with parchment paper. Set aside.
Add butter, granulated sugar, and brown sugar to medium mixing bowl. Beat together with an electric mixer until light and fluffy. Add egg yolk and vanilla extract and beat until both are mixed in.
In a separate small mixing bowl, whisk together the flour, baking powder, baking soda and salt. Slowly add flour mixture to butter mixture and blend in with an electric mixer on low speed or by hand just until a dough forms. See note if you have trouble getting the dough to form (you may have added a little too much flour and or your egg yolk may not have been large enough).
Stir in mini M&M candies until they are spread throughout the dough. Divide dough into 12 mounds using a medium (#40, 1½ tablespoon) cookie scoop and place each ball on the parchment lined air fryer tray or basket. Allow an inch or more of spacing. If needed, roll into balls with your hands keeping the candies within the dough. I also like to reserve some candies to press onto the top of the balls.
Preheat the air fryer to 220°F (105°C). Air fry for 7 to 12 minutes until the edges of the cookies are set. Air fry less for soft cookies and more for crispy cookies.
Remove air fryer tray or basket and place on a cooling rack. Once cool, remove cookies from the parchment paper.
Notes
The recipe was tested in an air fryer oven made by Cosori. Other styles/brands can vary slightly so you may not be able to fit all 12 cookies in at once. In that case, you can air fry in two separate batches of six cookies.Cookies can be baked in a 350°F oven instead of an air fryer. Baking time should still be between 7 and 12 minutes depending on texture desired. Bake longer for crisper cookies.If you have trouble getting the dough to form after adding the flour mixture to the butter mixture, you can add a little liquid, 1 teaspoon at a time. I generally add a little bit of the egg white leftover from separating out the yolk. But, you can also use milk or water.The dough can be refrigerated or frozen to use later. It’s best to use it up within 5 days of refrigerating or 3 months from freezing. However, the cookie dough should be fine to freeze for up to a year.