Preheat your oven to 350°F (175°C) and prepare your muffin tin with cupcake liners.

In a large mixing bowl, cream together the softened butter and granulated sugar for 3-4 minutes until light and fluffy. Add the eggs one at a time, mixing well after each addition, then stir in the vanilla extract.

In another bowl, whisk together the gluten-free flour, baking powder, baking soda, and salt. Gradually add this dry mixture to the wet ingredients, alternating with the buttermilk. Mix until just combined, then gently fold in the rainbow sprinkles.

Divide the batter evenly among the cupcake liners, filling each about two-thirds full.

Bake for 18-20 minutes, checking for doneness with a toothpick.

Allow the cupcakes to cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.

Beat the softened butter for the frosting until creamy, then gradually add the powdered sugar, mixing until well combined. Stir in the vanilla extract and add heavy cream until desired consistency is reached. Frost the cooled cupcakes and decorate with extra sprinkles.