This recipe comes from Harry's Roadhouse Cookbook.
1 Vidalia onion
1 cup buttermilk
3/4 cup flour
3/4 cup cornmeal
Salt to taste
1/4 tsp. pepper
Cut onion into very thin rings (1/8" or thinner). Soak onion in buttermilk for at least 2 hours or overnight.
When you are ready to cook, drain the onions in a colander.
Heat about an inch of oil in a cast-iron skillet.
Mix together flour, cornmeal, salt, and pepper in a mixing bowl. Toss the drained onion rings in this mixture until they are thoroughly coated. Shake off excess coating and fry the rings until they are crispy and golden. Drain on paper towels. These onion rings may be fried up to half an hour before serving.