Vegan Gluten Free Onion Rings

Adapted from Minimalist Baker

1 cup oat flour
1/4 cup cornmeal
1/4 cup cornstarch
1 teaspoon sea salt 
1 teaspoon Old Bay seasoning
black pepper, more or less to your liking
1 cup unsweetened plain plant milk
2 medium yellow onions, sliced into 1/2-inch rings
Avocado oil for frying

1. Heat oven to 225°F and line 2 baking sheets with parchment paper. Place one in the oven and one on the counter. Also set out a plate layered with a few paper towels.
2. In a large shallow bowl, mix together oat flour, cornmeal, cornstarch, salt, pepper, and Old Bay seasoning. Add milk to a separate small bowl.
3. One at a time, dip the onion rings in the dry ingredients first, then the milk, then back in the dry ingredients until well coated. Place on the parchment-lined baking sheet on the counter and repeat until all rings are coated. You can overlap them a little.
4. Heat a large cast iron or heavy skillet over medium heat and add enough oil to form a scant 1/2-inch layer. Heat for 3-5 minutes, or until a little flour sprinkled in bubbles and browns. Add some onion rings, only as many as will fit comfortably in the pan.
5. Fry on both sides for 1-2 minutes until golden. Use tongs or a fork for carefully flipping as the coating is somewhat fragile.
6. Transfer cooked onion rings to the paper-towel lined plate to blot off extra oil, then onto the parchment-lined baking sheet in the oven to keep warm. Continue until all onion rings are cooked. Serve hot with ketchup.