Sprinkle grated zucchini with 1/2 tsp salt and let sit for 10 minutes. Then spread out onto a kitchen towel and gently press the zucchini to get as much excess moisture out as you can.
Heat butter in skillet and sauté onion and garlic for a few minutes. Then add corn and continue cooking until onions are soft. Se aside to cool a bit.
In a small bowl combine the cornmeal, flour, cornstarch, baking powder and seasonings. In a large bowl combine the milk and egg, then add in the onion mixture. Mix well, then stir in the flour mixture until just combined.
To fry fritters; heat some oil in a skillet and spoon a heaping tablespoon of mixture into hot skillet (flatten out). When bottom turns golden brown, flip.
Serve with GF sour cream if you like.
Notes
To Make Buttermilk: put 1 tsp vinegar into measuring cup and add whole milk (or milk alternative) to bring to 3/4 cup - let stand 5 minutes.