Prepare the Cupcake Tins and Preheat the Oven - Line two cupcake tins with liners. Preheat the oven to 350 degrees Fahrenheit.
Cream Butter and Sugar - In a large bowl with an electric mixer, cream together the butter and sugar. Mix until they are fully combined and are light and fluffy in texture.
Add the Eggs and Vanilla - Once the butter and sugar have been creamed, add the eggs in one at a time. Beat well after each addition. Next, add the vanilla and mix until fully incorporated.
Mix the Dry Ingredients - In a medium bowl, use a whisk to combine the gluten-free all-purpose baking flour, baking powder, xanthan gum, and salt.
Add the Dry Ingredients and Milk to the Creamed Mixture - Alternate adding the dry ingredients and milk to the creamed mixture, beating well after each addition. Mix until just fully combined.
Bake the Gluten-Free Vanilla Cupcakes - Fill the cupcake liners 3/4 full with batter. Bake them for 15-20 minutes, or until a toothpick inserted into the center comes out clean. Cool the cupcakes in the pans for 10 minutes before moving them to the wire racks to cool all the way.
Make the Frosting - In a large bowl, use an electric mixer to beat the butter, cream cheese, confectioners’ sugar, and vanilla until smooth. Slowly add in enough milk until it reaches your desired consistency. Once the cupcakes are fully cool, decorate them with the frosting.