1 5/8 cup all purpose gluten free flour
3/4 teaspoon xanthan gum (omit if your blend already contains it)
6 tablespoons cornstarch
1/2 teaspoon baking soda
1 teaspoon baking powder
1/2 teaspoon kosher salt
1 cup granulated sugar
Zest of 1 large lemon
2 cups grated zucchini
2 eggs at room temperature, beaten
5 tablespoons neutral oil (like vegetable, canola or peanut oil)
3 tablespoons freshly squeezed lemon juice (from 1 large lemon)
1 1/2 cups confectioners’ sugar
1 1/2 tablespoons freshly squeezed lemon juice, plus more by the 1/4 teaspoonful if necessary
Preheat your oven to 325°F. Grease a standard 9-inch x 5-inch loaf pan and set it aside.
Prepare the batter. In a large bowl, place flour, xanthan gum, cornstarch, baking soda, baking powder, salt and sugar, and whisk to combine well. Add the lemon zest, and whisk until evenly distributed throughout the mixture, breaking up any lumps in the zest. Place 1 1/4 cups (125 g) of the grated zucchini on a large paper towel, fold over the towel and squeeze the zucchini once firmly to release some of the moisture. The zucchini should now weigh about 100 grams. Add it to the dry ingredients and mix to combine. Set the dry ingredients aside. Place the remaining 3/4 cup (75 g) of grated zucchini, along with the eggs, oil and lemon juice in a blender, and pulse until well-blended and beginning to emulsify. Create a well in the center of the bowl of dry ingredients, add the wet ingredient mixture. The batter will be thick. Scrape it into the prepared loaf pan, and smooth the top with a wet spatula.
Bake the bread. Place the loaf pan in the center of the preheated oven. Bake, rotating once, until the top is lightly golden brown and a toothpick inserted in the center of the loaf comes out with a few moist crumbs attached (about 50 minutes). Remove from the oven and allow to cool for at least 30 minutes in the loaf pan before transferring to a wire rack to cool completely.
Make the glaze. In a medium-size bowl, place the confectioners’ sugar and 1 1/2 tablespoons lemon juice. Mix well, until a thick paste forms. Add more lemon juice by the 1/4-teaspoon, mixing to combine well, until the glaze falls off the spoon slowly, in a thick but pourable glaze. Add liquid very slowly, as it is much easier to thin, than to thicken, the glaze. If you do thin the glaze too much, add more confectioners’ sugar a teaspoon at a time to thicken it. Pour the glaze over the top of the cooled bread and, using a small offset spatula or large knife, spread into an even layer. Allow the glaze to set at room temperature before slicing the loaf thickly and serving.