Cream together the butter and sugars in a mixer for 3 minutes. Add the eggs and vanilla, making sure to scrape down the sides of the mixing bowl. Add the flour, salt, baking soda and baking powder and mix on low until everything is incorporated. Fold in half of the M&M’s.
Chill the dough for at least 2 hours.
Preheat your oven to 350 degrees
Scoop out 2 tablespoons of dough, and roll it into a ball.
Place 12 of the cookie dough balls on a parchment lined baking sheet. Add a few M&M's on top of each cookie, making sure the M&M's stick into the dough.
For cookies that are soft in the middle (that’s how I like them) bake for 10-12 minutes until just slightly golden around the edges. If you want them crisp, bake for 12-14 minutes. Remove from the oven and let rest for 5 minutes before transferring them off the baking sheet and onto a cooling rack.