Prepare the zucchini by grating and spreading over flat surface lined with paper towels. Place another layer of paper towels over zucchini and press to squeeze out excess moisture. Let sit 10 minutes and set aside.
In a frying pan over medium heat, melt butter and sauté onions, corn, and minced garlic 3-5 minutes until tender.
In a mixing bowl whisk together flour, cornmeal, cornstarch, salt, and pepper together.
Add in zucchini, onion and corn mixture, cheese, egg, and milk. Mix until combined into a thick batter.
In same frying pan (wiped out) heat oil (about ¼ inch deep) over medium heat. Spoon ¼ cup batter at a time into pan. Cook 3-4 fritters at a time for 3-4 minutes on each side until golden brown.
Lay on paper towels to drain excess oil and serve while warm.
Notes
Drying the zucchini thoroughly ensures the fritters not falling apart as they are cooked due to excess moisture.If using frozen corn make sure it's completely thawed and excess moisture is drained just like the zucchini. To freeze, cool completely and freeze in an airtight container for up to 3 months.