Step 1

Preheat oven to 350°F. Line a baking sheet with parchment paper and set aside.

Step 2

In the bowl of your stand mixer fitted with the paddle attachment mix the butter, granulated sugar, light brown sugar, and molasses together for 2 minutes.

Step 3

Add the eggs, salt baking soda, baking powder, and cinnamon and mix for 1 minute, scraping the sides of the bowl as necessary.

Step 4

Turn the mixer to low and add in the flour and oats, mixing until combined.

Step 5

Using a medium (2- tablespoon) cookie scoop drop the dough on to the prepared baking sheet 3- inches apart. These cookies will spread.

Step 6

Bake for 10-12 minutes until the edges are golden and centers are just set.

Step 7

Allow the cookies to cool on the baking sheet for at least 5 minutes before transferring to a wire rack, carefully, to cool completely. The centers of the cookies will (and should be) very soft, which is why letting them cool on the baking sheet is an important step.

Step 8

In a small bowl, sprinkle the gelatin over 1/3 cup water. Stir it together and let it stand about 5 minutes. Mixture will get thick as it sits.

Step 9

In a 2- quart saucepan over medium-high heat, stir together the granulated sugar, corn syrup, and 1/4 cup water until mixture comes to a full boil. Continue boiling for 30 seconds and immediately remove the pan from the heat.

Step 10

Stir in the vanilla and gelatin mixture until it dissolves completely.

Step 11

Transfer the mixture to the clean bowl of your stand mixer fitted with the whisk attachment. With your mixer on medium speed, mix for 20 seconds. Gradually raise the speed to high and mix until the mixture is stiff, white, fluffy, and cooled to barely warm,  5-7 minutes.

Step 12

Reduce the mixer speed to low and gradually add your powdered sugar, mixing until incorporated. Then add the butter and turn the mixer up to medium speed and mix until completely smooth, about 2 minutes.

Step 13

The filling will set up as it sits, so wait until it is thick enough to spread or pipe before filling the cookies, 5-10 minutes. Make sure not to let it sit too long, as it will become too thick and marshmallow-like to spread.

Step 14

Use a large piping tip or an offset spatula to spread about 2 tablespoons of filling onto the bottoms of half the cookies. Press the remaining cookies onto the filling, creating sandwiches.

Step 15

Allow the cookies to set for 20-30 minutes.