Soft and chewy peanut butter oatmeal cookies filled with tons of delicious peanut butter and chocolate flavors, and sandwiched with a creamy and delicious peanut butter buttercream frosting. Everyone will love these easy and delicious monster sandwich cookies for any occasion.
The cookie dough is made just like a classic monster cookie dough filled with M&Ms and chocolate chips. Let the cookies cool completely before frosting with frosting. Make the filling by mixing all of the ingredients together until smooth. Spread it onto half of the cookies, then sandwich with the remaining cookies.

Ingredients
Method
- Preheat the oven to 350 F. In a medium bowl, whisk together flour, oats, salt, and baking soda. In a large bowl, mix together butter, peanut butter, granulated sugar and brown sugar until combined. Add in the egg and vanilla extract until smooth.
- Add in the flour mixture, mix until it is fully combined. Fold in the chocolate chips and M&Ms. Use a cookie scoop to place the cookies onto a large ungreased baking sheet at least 2-inches apart. Bake for 10-12 minutes. Let cool completely.
- In a large bowl, mix together butter, peanut butter, powdered sugar, and vanilla extract until smooth. Spread frosting onto half of the cookies, and sandwich with the remaining half.
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