In a large mixing bowl, whisk together 1 ¾ cups of all-purpose flour, 1 teaspoon of baking soda, 1 teaspoon of salt, 1 teaspoon of ground cinnamon, and ½ teaspoon of pumpkin pie spice along with 3 cups of old-fashioned oats. Mix until well combined.

In your stand mixer, fitted with the paddle attachment, beat together 1 cup of room-temperature unsalted butter, 1 cup of packed brown sugar, and ½ cup of white granulated sugar on high speed for about 2 minutes until light and fluffy.

Next, add in 1 teaspoon of pure vanilla extract, ½ tablespoon of molasses, and 2 large eggs. Mix on medium speed until fully combined.

Gradually incorporate your dry mixture into the wet ingredients, mixing on low speed until just combined.

Chill the dough in the refrigerator for about 15 minutes while preheating your oven to 350°F (175°C) and lining two baking sheets with parchment paper.

Use a cookie scoop to portion out the dough, forming approximately 36 cookies, and place on baking sheets.

Bake the cookies for 8–9 minutes, or until just set and lightly golden around the edges. Allow to cool for 4 minutes on the baking sheet before transferring to a wire rack.

In a clean mixing bowl, beat together 1 cup of room-temperature unsalted butter and 7 ounces of marshmallow fluff on high speed until light and fluffy.

To the butter and fluff mixture, add 1 cup of sifted powdered sugar, 1 teaspoon of vanilla extract, and ¼ teaspoon of salt. Mix on low speed until combined, then increase to high speed for another 4 minutes until airy and spreadable.

Assemble the Oatmeal Cream Pies by spreading a generous amount of the marshmallow filling onto one cookie and sandwiching with another cookie.

Chill the finished pies in the freezer for at least 10 minutes to let the filling set.

Store any leftovers in the refrigerator in an airtight container.