M & M Cookie Sandwiches

Name: M & M Cookie Sandwiches
Cuisine: American
Ingredients: 1 1/2 cups flour (all purpose); 1 teaspoon baking powder; 1/2 teaspoon baking soda; 1/4 teaspoon salt; 1 stick unsalted butter (room temperature); 1/2 cup granualted sugar; 1/3 cup brown sugar; 1 large egg; 2 teaspoons vanilla; 8 ounces M&M's (1- 8 ounce bag); 2 sticks unsalted butter (room temperature); 1 pound powdered sugar; 4 tablespoons heavy cream