Preheat the oven to 180 ℃ (356 ℉)

Add and combine, the white rice flour, tapioca flour, corn starch, brown rice flour, baking powder, salt, baking soda and xanthan gum. Set the dry ingredients aside.

In a stand-alone mixer with the paddle attachment or a hand-held mixer, beat the vegetable oil and sugar until light and fluffy (2-3 minutes).

Next, add the eggs one at a time and mix until combined. Then add the vanilla extract, lemon zest, and fresh lemon juice and beat until combined.

Add half of the dry ingredients to the wet ingredients, followed by the buttermilk and beat until combined. Then add the remaining dry ingredients and beat until just combined.

Grease your bundt pan with butter and add your cake batter until the pan is ⅔ full.

Place your bundt pan in the oven on the center rack and bake it for 30-33 minutes or until a toothpick inserted at the middle comes out clean. Let the cake sit in the bundt pan for 10 minutes before inverting it.

In a bowl, add the powdered sugar, lemon juice, lemon zest, and heavy cream. Then using a whisk, combine the ingredients. If the glaze is too thin, you can add more powdered sugar, and if the glaze is too thick, add more heavy cream.

Once the cake has cooled down, pour the glaze on the cake and let it sit for about 30 minutes.