In a separate bowl, whisk together the flour, baking soda, salt, and cinnamon.
4 Add the dry ingredients to the wet mixture and stir until just combined.
5 Fold in the quick oats evenly.
6 Cover and chill the dough for 20 minutes.
7 Preheat oven to 350°F (175°C) and line a baking sheet with parchment paper.
8 Scoop dough into 1-inch balls and place them 2 inches apart.
9 Bake for 9–11 minutes until the edges are golden and centers are set.
10 Let cookies cool on the tray for 5 minutes, then transfer to a wire rack.
11 For the filling, beat softened butter until smooth.
12 Add powdered sugar gradually, then mix in marshmallow fluff and vanilla extract.
13 Add milk if needed to loosen the texture. Chill the filling for 10 minutes.
14 Pipe or spoon the filling onto half the cookies, then top with the rest.
15 Optional: roll the cookie edges in sprinkles or colored sugar.
Note
- For best texture, use quick oats, not rolled oats.
- Make them baby shower–themed by tinting the cream filling with pastel food coloring.
- Use cream cheese instead of marshmallow fluff for a tangy twist.
- Cookies stay fresh for 2–3 days in an airtight container. If using cream cheese, store in the fridge.