In a large mixing bowl, combine rolled oats, milk, molasses, and vegetable oil. Let sit for 30 minutes.

Preheat your oven to 350°F (175°C) and prepare two cake pans.

In a separate bowl, whisk together flour, baking powder, baking soda, cinnamon, and salt.

In a stand mixer, beat softened butter and sugars until light and fluffy. Add eggs one at a time.

Alternate adding the dry mixture and soaked oat mixture to the creamed butter until combined.

Divide the batter into prepared pans and bake for 30-35 minutes.

Let the cakes cool in the pans for 10 minutes, then transfer to a wire rack to cool completely.

To make frosting, beat butter, then gradually add powdered sugar and cream until smooth. Add vanilla bean paste.

Mix marshmallow fluff with a portion of the frosting for filling.

Assemble the cake by leveling tops, layering with filling, and frosting the exterior.

Garnish with oatmeal cream pies before serving.