Preheat oven to 350°
Line baking sheets with foil or parchment paper and grease lightly
Melt the butter and let cool slightly before adding to mixing bowl
Mix butter and sugars on medium speed until combined
Add eggs and peanut butter and mix on medium speed until well combined, scraping edges of bowl.
Add dry ingredients and mix until just combined. Don't overmix.
Add M&M candies and mix on low speed until candies are incorporated
Cover bowl with plastic wrap and place in fridge for 30 mins to an hour
Remove from fridge and scoop by heaping tablespoonfuls and place on prepared baking pan about 2 inches apart
Bake for 16-18 minutes or until cookies have browned lightly and have begun to crack on the top
Remove from oven and let cool on baking sheet for 1-2 minutes before removing to cooling rack.
Cool completely and store in an airtight container