2. Spray an 8½x4¼x2½-inch loaf pan with canola oil.
3. Sift the flours, baking powder, xantham gum and salt in a bowl.
4. Whisk together the yogurt, sugar, eggs, lemon zest and vanilla.
5. Mix in the flour, alternating with the oil. Mix until combined.
6. Pour into baking pan and bake for about 45 minutes or until a knife placed in the center of the cake comes out clean.
7. While the cake is baking, make the lemon sauce. Heat the sugar and lemon juice in a small saucepan until the sugar melts and the sauce is clear. Don't overcook. Set aside.
8. When the cake is done, let it cool for about 10 minutes. Take it out of the pan and place on a cooling rack with a cookie sheet or plate underneath (I used parchment to hold the cake in my hand as I turned it over and then flipped it onto the cooling rack.) Pour the lemon sauce over the warm cake.
9. Let the cake cool. Mix together the lemon juice and powdered sugar until there are no lumps. Once the cake is cooled, pour the glaze over the cake.