If you’re using an electric hand mixer, switch to a wooden spoon to stir in the chocolate chips and M&Ms. Trying to beat the chocolate into the thick dough can put too much stress on a hand mixer.
Dipping your fingertips in a bowl of cold water, before pressing the cookie dough around the pan, makes the sticky batter more manageable.
Removing the chocolate topped bar from the freezer after 30 minutes makes it easier to cut the dessert into pieces. You can leave the cookie dough bites in the freezer longer, but the chocolate-peanut butter topping will be firmer and tend to crack when you cut it up.