Step 1

Line baking sheets with parchment paper. Set aside.

Step 2

In the bowl of a stand mixer with a paddle attachment (or a handheld mixer), beat the butter on medium-high speed until smooth (about a minute).

Step 3

Add the peanut butter; beat for about 2 minutes, or until smooth.

Step 4

Add brown sugar and cream on medium-high speed until smooth (about 2 minutes).

Step 5

Add eggs, one at a time, mixing for 30 seconds after each addition. Scrape down the sides of the bowl and beat ingredients together again, if necessary.

Step 6

With the mixer off, add the flour, oats, baking soda, and salt. Mix on low until just combined, being careful not to overmix.

Step 7

With the mixer still on low (or by hand), add the M&M's and chocolate chips and mix until incorporated. (If using an electric mixer, only mix for a few seconds.)

Step 8

Drop spoonfuls (2-3 tablespoons) of dough onto the lined baking sheets about 2 inches apart. (If possible, measure the batter so the cookies are all the same size for best results when baking.) Top with mini m&m's (optional).

Step 9

Place the baking sheets of unbaked cookies into the refrigerator to chill for about 30 minutes. (If letting the dough chill overnight, be sure to cover.)

Step 10

When ready, preheat the oven to 350°F. Remove the cookies from the refrigerator.

Step 11

Bake the cookies for 10 minutes. The cookies are done when the sides are lightly browned and the centers still look soft.

Step 12

Remove from the oven and let cookies cool on the baking sheet for a few minutes before transferring to a wire rack to finish cooling.