This gluten-free Funfetti cake recipe is made easy with a food processor. Combine gluten-free flour, sugar, baking powder, and salt in the food processor, then add in butter, eggs, vanilla extract, and milk. Pulse until the batter is smooth, then fold in rainbow sprinkles. Bake in a preheated oven for 25-30 minutes, or until a toothpick inserted in the center comes out clean. Let cool before frosting with a gluten-free vanilla buttercream.