PREPARE THE CUPCAKE BATTER

1. Preheat the oven to 325F and line a standard muffin tin with paper liners.
2. In a large mixing bowl (or the bowl of a stand mixer), whisk together the gluten-free 1:1 flour, sugar, cornstarch, baking powder, baking soda, and salt.
3. Sprinkle the cubed butter on top of the dry ingredients and use an electric hand mixer (or a stand mixer with the paddle attachment) to beat the butter into the dry ingredients until the butter is fully incorporated (start with the mixer on low and increase to medium-high). The mixture should look like coarse bread crumbs and there will be no visible pieces/chunks of butter.
4. Add the oil and mix on low to combine (it will look coarse and crumbly.)
5. Add the egg, sour cream, milk, and vanilla bean paste and mix on low until combined. Then turn the mixer up to medium and mix until the batter is mostly smooth.

BAKE THE CUPCAKES

1. Distribute the batter evenly between the muffin liners, filling each about 2/3 full (there should be 14 cupcakes total).
2. Bake on the center rack of the oven for 18-22 minutes or until the tops of the cupcakes spring back when gently touched. A toothpick inserted in the center should come out clean or with a few moist crumbs.
3. Allow the cupcakes to cool in the pan for 5 minutes before carefully removing them and placing on a wire rack to continue cooling.

PREPARE THE FROSTING

1. Place the butter in a large mixing bowl (or the bowl of a stand mixer) and use an electric hand mixer (or the paddle attachment of the stand mixer) to mix the butter until completely smooth and creamy.
2. Gradually add the powdered sugar 1 cup at a time (start with 4 cups and add more powdered sugar after adding the milk if needed). Mix well between each addition and scrape down the sides and bottom of the bowl as needed.
3. Add the milk, vanilla bean paste and salt and mix until light and fluffy (start with 2 tbsp of milk and increase as needed to get desired consistency)

FROST THE CUPCAKES

1. Place the frosting in a piping bag with a large round tip and pipe a generous amount of frosting on each cupcake. Use an offset spatula or butter knife to swirl the top of the frosting slightly.
2. Garnish with sprinkles and enjoy!