Preheat the oven to 350°. Butter and flour a bundt pan, set aside. Be sure to get all the nooks and crannies of your pan as the cake will stick.
In a medium bowl, whisk the GF flour, cornstarch, xanthan gum, baking powder, baking soda, and salt. Set aside.
Peel the yellow rind off of the lemons. You do not want to remove as little of the white part as possible. Place the yellow part only and the sugar in a food processor and pulse until the lemon peel is broken up. Set aside.
Cut the lemons and half and juice. You need ½ cup of juice. Save the remaining juice for the glaze. In a small bowl, whisk ½ cup of lemon juice with the yogurt. Set aside.
In a large bowl, using an electric mixer, beat the butter with the sugar mixture at medium-high speed until fluffy, about 2 minutes. Add the eggs and beat on medium until incorporated.
Add ⅓ of the dry ingredients, beat until in incorporated. Add ⅓ of the yogurt mix and beat until incorporated. Alternate until both are used up. Scrape down the sides of the bowl, and give a quick mix to make sure all of the ingredients are well incorporated.
Pour the batter into the prepared pan and allow to rest for 10 minutes. Bake for 50 minutes, until the cake is golden and a tester comes out clean.
Set the cake on a cooling rack. Carefully run an offset spatula or table knife around the center of the pan to loosen the cake. Cool for 20 minutes, then unmold and fully cool.
Glaze
Place confectioners' sugar in a liquid measuring cup; stir in lemon juice (glaze should be thick, yet pourable). Add more sugar or lemon juice, as necessary, to achieve a pourable consistency.
Pour over the cooled cake. Allow to set for 30 minutes for the glaze to harden.
Notes
Substitutions:
Sour cream can be substituted for yogurt.
Limoncello can be substituted for lemon juice in both the loaf and the glaze.
An additional ¼ cup of GF flour or almond flour can be used in place of the cornstarch but the cake will be denser.
Make Ahead: This recipe can be made up to 2 days in advance. Tightly wrap the baked, but unglazed loaf, in plastic wrap and place it in a plastic bag. Bring to room temperature before glazing and serving.Freeze: Tightly wrap the baked, but unglazed loaf, in plastic wrap and place it in a freezer bag. It will keep for two months. Thaw in the refrigerator overnight and bring to room temperature before glazing and serving.