Add and whisk the white rice flour, tapioca flour, corn starch, brown rice flour, xanthan gum, baking powder, salt, and baking soda. Set the dry ingredients aside.
Using a standalone mixer, with the paddle attachment fitted or handheld mixer, beat the butter, cream cheese, sugar at medium-high speed until creamy (1-2 minutes). Then add the eggs one at a time, mixing until incorporated with each addition. Then, add the vanilla extract and mix until combined.
Add ⅓ of dry ingredients followed by ⅓ of the Buttermilk and mix until combined. Repeat two more times until the vanilla cake batter is formed (1-2 minutes). Do not overmix the batter. The cake batter will be thick.
Grease a standard-size Bundt pan with butter. Pour the cake batter into the Bundt pan and bake the gluten free vanilla cake for 35-40 minutes or until a toothpick inserted at the center comes out clean.
Let the cake cool down in the Bundt pan for 10-15 minutes before inverting it. Then, flip the cake onto a cooling rack and let it cool down to room temperature before storing.
Notes
Flour Mix: You can substitute 320 grams (2.5 cups) of gluten-free all-purpose flour (see recommended brands above) for white rice flour, tapioca flour, corn starch, and brown rice flour. If your flour blend has xanthan gum, omit it.
Dairy-Free Option: This cake can be dairy-free by using vegan cream cheese and dairy-free Buttermilk. Add 1 ¼ tablespoon of lemon juice or white vinegar to 256 ml of almond or coconut milk to make dairy-free Buttermilk. Let the Buttermilk sit for 10 minutes or until it thickens before using it.
Storage: The gluten-free vanilla cake can be stored in the fridge in an air-tight container for up to a week and up to three days at room temperature.