Preheat the oven to 350°F. Spray a 9″ springform pan with (gluten free) cooking spray and line with parchment. Spray again and set aside.

Add the sugar, lemon zest and minced rosemary to a large mixing bowl. Using your fingers, massage the zest and rosemary into the sugar until the sugar becomes a pale yellow color, is quite fragrant, and looks slightly moistened. Whisk in the brown rice flour, almond flour, baking powder, and sea salt until evenly combined. Add the eggs, olive oil, and buttermilk and whisk until smooth. Stir in the vanilla extract. Pour the batter into the prepared pan and place on a rimmed baking sheet. Bake for 35 minutes or until a toothpick inserted into the center of the cake comes out clean.

Cool for 10 minutes in the pan, then run a sharp knife around the edge of the cake. Release the latch from the pan and remove. Cool the cake completely before glazing.

Make the glaze, whisk the powdered sugar with 3 tablespoons of lemon juice until smooth. Add the salt and whisk well to combine. If the glaze seems too thick to pour, add a little more lemon juice and whisk to combine. Place the cake on a rack over a pan. Drizzle the glaze evenly over the cake. It will set in a few minutes.