Ingredients:

  • 1 cup (2 sticks) softened unsalted butter (for cookies)
  • 1 cup packed brown sugar
  • 1/2 cup granulated sugar
  • 2 large eggs
  • 1 tsp vanilla extract (for cookies)
  • 2 cups all-purpose flour
  • 1 tsp baking soda
  • 1/2 tsp salt
  • 1 1/2 tsp cinnamon
  • 2 1/2 cups quick oats
  • 1 cup (2 sticks) softened unsalted butter (for filling)
  • 3 cups confectioners' sugar
  • 7 oz jar marshmallow fluff
  • 1 tsp vanilla extract (for filling)
  • 2 tbsp heavy cream

Instructions:

  1. Beat the softened butter, brown sugar, and granulated sugar together until the mixture is light and fluffy (3–4 minutes). This step is crucial for aerating the fat for a soft cookie.
  2. Introduce the two eggs one at a time, followed by the vanilla extract. Scrape down the sides of the bowl thoroughly after each addition.
  3. In a separate bowl, whisk the flour, baking soda, salt, and 1 ½ tsp of cinnamon.
  4. Gently mix the dry ingredients into the wet mixture on the lowest speed until just combined. Stop the moment you see no dry streaks.
  5. Stir in the quick oats by hand to prevent overmixing and gluten activation.
  6. Use a small cookie scoop (1.5-2 tbsp) to portion out all 36 dough balls onto a tray. Cover and chill for a minimum of 45 minutes to prevent spreading during baking.
  7. Preheat your oven to 375°F (190°C). Arrange the chilled dough balls 2 inches apart on parchment-lined baking sheets. Bake for 8–10 minutes until the edges are set and lightly golden brown, but the centers should still look slightly underdone.
  8. Let the cookies rest on the hot pan for 5 minutes, then transfer them to a wire rack to cool completely. They must be cold before filling.
  9. Beat the softened butter (for the filling) until truly creamy and light in color.
  10. Gradually add the confectioners' sugar. Once incorporated, add the full 7 oz jar of marshmallow fluff. Whip on medium-high for 2 minutes until the mixture is light and voluminous.
  11. Beat in the vanilla and heavy cream until the filling is pillowy soft, easily spreadable, but thick enough to hold its shape.
  12. Match your cooled cookies by size. Pipe a generous 1–2 tablespoons of the cream filling onto the flat side of one cookie. Gently press the matching cookie on top until the filling spreads to the edges.