Preaheat oven to 350°. Line two cookie sheets with parchment paper.

Mix butter, 1/2 cup powdered sugar, and vanilla with an electric mixer until fluffy. Add flour, salt and mix until the dough comes together. **This will take a minute or two with a stand mixer. If you’re using a hand mixer it can take even longer. Get your hands in there if it’s not mixing up. Eventually it WILL come together like a cookie dough.** Stir in the M&Ms.

Scoop 1 tablespoon balls of dough and place on prepared cookie sheet.

Bake cookies for 8-10 minutes until bottoms are just slightly brown. Remove from oven and cool for just 5-10 minutes, until you can handle them. Fill a small bowl with powdered sugar and roll each cookie in the sugar until coated. Place on a rack to cool. (Once cookies are cooled, you may want to re-roll them in more powdered sugar.)

Cookies can be frozen for up to one month (you may need to re-roll them in powdered sugar after defrosting). Store in an airtight container.