For the Pumpkin Cupcakes

1. Preheat your oven to 350 degrees Fahrenheit. Add liners to a 12-cavity muffin tray.
2. In a medium bowl, whisk all purpose flour, baking soda, salt, cinnamon, and nutmeg together with a whisk until combined.
3. In a large bowl, whisk vegetable oil, room temperature egg, light brown sugar, granulated sugar, and pumpkin puree together with a whisk until smooth.
4. Add dry ingredients to the wet ingredients, using a whisk to carefully combine the two. Use a spatula to scrape down the sides and bottom of the bowl to ensure all of the ingredients are fully incorporated.
5. Divide batter between the 12 liners, about 1/4 of batter per liner. The liners should be about 2/3 full.
6. Bake for 18-24 minutes or until the tops of the cupcakes are set, the centers spring back when poked with your pointer finger, and a toothpick inserted into the center comes out with moist crumbs.
7. Allow the cupcakes to cool before frosting. Prepare frosting as they cool.

For the Marshmallow Frosting 

1. In a large bowl with a hand mixer or in the bowl of your stand mixer fitted with the paddle attachment, beat butter on medium speed until smooth.
2. Slowly, add the powdered sugar to the butter while mixing on low speed. Use a spatula to scrape down the sides of the bowl as needed.
3. Add marshmallow fluff to the mixture on medium speed and beat until smooth. Pour the heavy whipping cream into the frosting and beat on medium high speed for two minutes until smooth and velvety.
4. Transfer frosting to piping bag fitted with a piping tip of your choice or frost with a knife or spoon. Store cupcakes tightly covered or in an airtight container at room temperature for up to 2 days or in the fridge for up to 4 days.