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Chewy Black + White Chip Oatmeal Sandwich Cookies with Marshmallow Buttercream Filling

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  • 1/2 cup unsalted butter, at room temperature
  • 1/2 cup sugar
  • 1/2 cup loosely packed brown sugar
  • 1 large egg
  • 2 teaspoons vanilla extract
  • 1 1/4 cup all-purpose flour
  • 1/2 teaspoon baking soda
  • 1/4 teaspoon salt
  • 3/4 cups rolled oats
  • optional: 1-2 tablespoons milk, if dough is super crumbly
  • 2/3 cup dark chocolate chips
  • 2/3 cup white chocolate chips

marshmallow buttercream filling

  • 1/2 cup unsalted butter, softened
  • 1 cup marshmallow cream, homemade or store-bought is fine
  • 1/2 cup powdered sugar
  • 1 teaspoon vanilla extract
  • 1 pinch of salt


  • Preheat the oven to 375 degrees F.
  • Add the butter to the bowl of your electric mixer and beat until creamy. Add in the sugars and beat on high speed until fluffy, about 2 to 3 minutes. Add the egg and vanilla, mixing well until combined, about 2 minutes. Stir in the flour, baking soda and salt with the mixer on medium speed. Beat in oats until just combined. Add in 1 tablespoon milk if the dough appears too crumbly. Fold in the chocolate chips. Refrigerate the dough for 30 minutes.
  • Roll the dough in to equally sized 1-inch balls and place them on a nonstick baking sheet 2 inches apart. Bake for 9 to 11 minutes, until the edges are just golden. Wait until the cookies cool COMPLETELY before adding the buttercream in the center and sandwiching the cookies together.

marshmallow buttercream filling

  • Add the butter to the bowl of your electric mixer and beat until creamy. Add in the marshmallow and beat on medium speed until the mixture comes together, about 2 minutes. Add in the sugar, vanilla extract and salt, mixing on medium speed for another minute. Scrape down the sides of the bowl and mix the buttercream on high for 2 to 3 full minutes.



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