Step 1

Preheat the oven to 350℉ (177℃). Line baking sheet pans with a silicone baking mat or parchment paper.

Step 2

In a mixing bowl, whisk together the all-purpose flour, baking powder, baking soda, cinnamon, and salt. Set aside.

Step 3

In the bowl of a stand mixer fitted with a paddle attachment or in a large bowl with an electric hand mixer, cream the unsalted butter, light brown sugar, and granulated sugar for a few minutes until light, pale, and fluffy.

Step 4

Add the eggs, one at a time, mixing in between each addition. Then, add the molasses and vanilla extract and mix well to combine.

Step 5

Add the flour mixture and quick oats and mix on the lowest speed until the ingredients are well incorporated and the cookie dough forms. Scrape the sides and bottom of the bowl to ensure the ingredients are well mixed.

Step 6

Portion the cookie dough using a large cookie scoop (3 tablespoons) and place the cookie dough balls on the prepared baking sheet pans. Allow plenty of space for spreading as the cookies will double in size.

Step 7

Bake the cookies for 10 to 12 minutes until the edges of the cookies are light golden-brown. Remove the pan from the oven. If the cookies are misshapen, use the back of a spoon or large round cookie cutter to immediately shape the cookies. Cool the cookies on the pan for 2 minutes and then transfer to a wire rack to cool completely.

Step 8

In the bowl of a stand mixer fitted with a paddle attachment or a large bowl with an electric hand mixer, cream the unsalted butter for a few minutes until light and fluffy.

Step 9

Add the marshmallow cream and mix on low speed until well combined. Then, add in the powdered sugar, vanilla extract, and salt. Mix on low speed until the ingredients are well incorporated. Scrape the sides and bottom of the bowl as needed.

Step 10

Turn the mixer to medium speed and whip the marshmallow cream filling for 2 minutes until it is smooth and creamy.

Step 11

Fill a piping bag with the tip cut off with the marshmallow cream filling. Pipe the marshmallow cream on the bottom of one of the cookies and top with another cookie to create a cookie sandwich. If you do not have a piping bag, you can use an offset spatula or butter knife to speed the marshmallow cream onto the cookies.