What is the only way to make a truly perfect cookie… better? Add buttercream. Peanut butter buttercream, to be exact. My Rainbow M&M Cookies are now MINI (i love cute things!!) and double stuffed, over-filled, and bursting with buttery, creamy peanut butter buttercream.
I have a love for the same basic cookie dough recipe, a recipe based off of the Cooks Illustrated recipe for Chewy Chocolate Chip Cookies. I’ve used the dough recipe for several of my recent cookies because…. it’s a guarantee. This basic recipe produces thick, chewy, unbelievably soft cookies.
The peanut butter buttercream filling is extremely decadent in today’s cookies. Like, hand-me-a-TALL-glass-of-milk-decadent. It’s rich and THICK. It’s much different than the silky peanut butter frosting I used to frost my brownie cupcakes. No, this buttercream is comparable to the thick sandwich filling in Oreos and I credit that to the smidge of heavy cream I used in my recipe. You may use any type of milk or even half-and-half, but I had leftover heavy cream in my fridge, so I figured what-the-heck!
A buttercream’s thickness is directly related to the ratio of liquid vs sugar.
I used very little heavy cream in this buttercream and a decent amount of confectioners sugar, thus producing a stick-to-the-roof-of-my-mouth frosting.
The mini M&Ms and peanut butter buttercream filling pair wonderfully together, just as one would imagine. Peanut Butter M&Ms are my favorite and I get the same fudgy/PB effect in today’s cookie recipe.
Mini Rainbow M&M Cookie Sandwiches with Peanut Butter Buttercream
Buttercream filled cookie sandwiches should be stored in the refrigerator.
Yield: 30 mini cookie sandwiches
- 2 cups + 2 Tbsp all-purpose flour
- 1/2 tsp baking soda
- 3/4 cup (1.5 sticks) salted butter, softened to room temp
- 1 cup light brown sugar
- 1/2 cup sugar
- 1 egg + 1 egg yolk, at room temperature
- 2 tsp vanilla extract
- 1.5 cups mini M&Ms
Peanut Butter Buttercream
- 6 Tbsp salted butter, softened to room temperature
- 6 Tbsp creamy peanut butter
- 2 tsp vanilla extract
- 3 cups confectioners’ sugar, sifted (plus extra if needed)
- 1 Tbsp cream or milk or half-and-half (plus extra if needed)
- Preheat oven to 325 degrees.
- Make the cookies. Mix the flour and baking soda in a bowl and set aside. With an electric or stand mixer fitted with a paddle attachment, cream the butter and sugars together on medium speed. Add the egg, egg yolk, and vanilla and mix well. Gradually add the flour mixture and stir until a dough forms. Fold in mini M&Ms.
- Chill dough for AT LEAST one hour (I chilled mine for 24 hours).
- Drop cookie dough into small uniform sized balls (mine were about 1 tsp of dough each, which are TINY, but bake them any size you'd like) onto ungreased baking sheet or silpat. Bake for 8-11 minutes or until edges are slightly browned. The centers should appear soft and puffy. Let cool completely on wire rack.
- Make the frosting. Cream butter and peanut butter on medium-high speed with a stand mixer fitted with a paddle attachment. Add vanilla extract and 2 cups confectioners' sugar. Beat for 2-3 minutes, or until mixture is smooth and thick. Scrape down the sides of the bowl if needed. Add milk/cream/half-and-half and beat for another minute. Add 1 more cup of confectioners' sugar and continue adding until you reached desired consistancy. I added exactly 3 cups. Once cookies are completely cooled, stuff cookies generously with peanut butter buttercream filling.
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Here are my original, full-sized, un-stuffed Rainbow M&M Cookies: