Preheat the oven to 375°. Using the paddle attachment for the mixer, cream together both types of sugar and the butter until the mixture is smooth and the ingredients are well incorporated with one another.

Add the peanut butter and mix until well incorporated then scrape the bowl.

With the mixer on low, add 1 egg at a time. Wait until the egg is incorporated then add the second egg and mix until incorporated.

Add the baking soda to the flour then add the flour to the mixer 1/2 cup at a time. Wait until the previous 1/2 cup is all mixed in before adding the next 1/2 cup. Once all of the flour is mixed in, take the bowl off the mixer and scrape down both the bowl and the paddle.

Add the M&Ms and mix them in by hand being careful not to overmix the cookie dough. Overmixing with result in a tough cookie.

Scoop the cookie dough using the ice cream scoop onto the parchment-lined cookie sheet about 3 inches apart.

I baked these cookies for exactly 12 mins. When they came out of the oven they didn't look or feel done but I let them continue to cook while they were cooling and they set up perfectly. I had previously baked them for 13 mins and they became hard and crunchy the next day. Baking them for 1 min less solved that problem completely. All ovens are different and you might have to do some experimentation with your bake time to find that sweet spot. Also, you don't need to make a whole sheet of cookies to find what time works best. Try baking one or two at a time.

Leave the cookies on the baking sheet and allow them to cool for 10 mins. Then transfer them to a cooling rack if they still need to cool.