For Cake Layers
2 1/2 cups Brown-Rice Flour Mix (recipe follows)
1/2 teaspoon salt
1 tablespoon baking powder
1 teaspoon xanthan gum
1 cup milk
1 cup canola oil, plus more for greasing pans
1 teaspoon pure vanilla extract
1 tablespoon finely grated fresh lemon zest
2 cups granulated sugar
4 large eggs

For Lemon Curd
2 teaspoons finely grated fresh lemon zest
1/4 cup fresh lemon juice
1/4 cup plus 2 tablespoons granulated sugar
3 large egg yolks
1/4 teaspoon guar gum
1/2 stick unsalted butter, cut into tablespoon pieces
1/4 teaspoon lemon extract

For Lemon Frosting
1 cup (2 sticks) unsalted butter, softened
3 1/2 cups confectioners’ sugar
1/4 cup fresh lemon juice
1/2 teaspoon lemon extract
2 teaspoons finely grated fresh lemon zest

Brown Rice Flour Mix
2 cups brown-rice flour (extra finely ground)
2⁄3 cup potato starch
1⁄3 cup tapioca flour