You will need:
1 cup (2 sticks) butter, softened
1 cup brown sugar, packed
1/ 2 cup sugar
2 large eggs, room temperature
1 teaspoon vanilla
1 1/ 2 cups all-purpose flour
3 cups old-fashioned oats
1 teaspoon baking soda
2 teaspoons cinnamon
Filling:
3/ 4 cup (1 1/ 2 sticks) butter, softened
3 cups confectioner’s sugar or icing sugar
1 jar (7 ounces) marshmallow creme
1-3 tablespoons whole milk

Method:
In your stand mixer fitted with a paddle attachment, add the butter and sugars. Cream for 2-3 minutes or until they are fully incorporated and fluffy. Add in the eggs and vanilla and mix until combined.

Turn the mixer off and add in the flour, oats, baking soda, and cinnamon. With the mixer on low, mix until just combined. Refrigerate for 30 minutes, or up to overnight.

When you are ready to bake the cookies, preheat oven to 350°F and prepare a baking sheet by lining it with parchment paper. Use a cookie scoop, table spoon or small ice cream scoop and drop dough onto the parchment-lined baking sheet about 2 inches between.

Bake for 8-10 minutes or until the edges are lightly golden. The top of the cookie may appear a little wet, but they will continue to bake out of the oven. You don’t want the cookies raw, so make sure they bake for at least 8 minutes. After allowing the cookies to slightly cool, move them to a cooling rack.

Filling:
While the cookies are cooling, mix together the butter, sugar, and marshmallow creme.
Add enough milk to make the filling spreadable. Spread filling on the bottoms of half the cookies and top with the remaining cookies.

Tip: You can use any filling