Line the bottom and sides of a 9"x13" baking pan with parchment paper.
Beat butter and brown sugar together until fluffy.
Add vanilla and beat until combined.
Mix in the gluten free flour and sweetened condensed milk and beat until smooth.
Add 1 & ½ cups chocolate chips and the M&Ms to the batter and beat until completely combined.
Place the mixture in the prepared pan and use your fingertips to press the dough evenly around the pan.
Cover the pan with foil and freeze for at least 2 hours.
Make the Topping:
Place a small, heat proof bowl, over a pan of simmering water. Add the ½ cup chocolate chips to the bowl and melt the chocolate.
Remove the bowl of melted chocolate from the pan and stir in the peanut butter until combined.
Take the foil off the frozen cookie dough and spread the chocolate-peanut butter topping over the top.
Place the foil back on the pan and freeze for 30 minutes.
Cut into pieces and serve.
Notes
Not all gluten free flour is intended to be a cup for cup substitute for all-purpose flour. I use Bob’s Red Mill Gluten Free 1 to 1 Baking Flour. If you use another gluten free flour blend your results may vary.
Heat-treat your flour before using it in this recipe. Heat-treating the flour will remove possible bacteria in raw flour.
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 dough around the pan, makes the sticky batter more manageable.
Removing the chocolate topped cookie dough from the freezer after 30 minutes makes it easier to cut the dessert into pieces. You can leave the pan in the freezer longer, but the chocolate-peanut butter topping will be firmer and tend to crack when you cut it up.