3/4 cup each sorghum flour, brown rice, and buckwheat flour
2 cups (packed) shredded zucchini
2/3 cup honey
1/2 cup melted butter
1 teaspoon vanilla extract
1-1/2 teaspoon baking powder
3/4 teaspoon baking soda
1-1/4 teaspoon salt
2 tablespoons cinnamon
1 cup chopped walnuts (optional)
In a medium bowl, mix sourdough starter, milk, and flours until combined into a stiff dough. Cover and allow to sour 6 to 12 hours, or overnight.
When ready to bake, preheat oven to 400°F.
Place shredded zucchini in a clean towel and squeeze as much moisture out as you can.
In a small bowl, beat the eggs and whisk in honey, melted butter, and vanilla. Stir in zucchini shreds.
Sprinkle the baking powder, baking soda, salt, and cinnamon over the soured dough. Pour the egg-honey mixture over this and mix in gently. Add the walnuts, if using, and finish mixing everything together until well combined.
Divide the batter amongst two buttered loaf pans, filling them half to two-thirds full each.
Place pans in the oven and bake for 40 minutes, or until the tops are set, the bottom has browned, and a knife inserted comes out clean.
Remove and allow to cool completely before slicing.