1 large Walla Walla or other sweet onion
1/2 c flour
1/4 c cornstarch
1/2 tsp baking powder
1/2 tsp salt
3/4 c beer
Flour for sprinkling on rings
Coconut oil for frying
Preheat oven to 250°F. Set a cooling rack over a rimmed baking sheet.
Cut onions crosswise into 1/2-inch thick slices and separate into rings. Reserve smaller inner rings for another use. Sprinkle rings with flour in a large bowl. Toss and let sit 30 minutes.
When ready to fry, whisk together 1/2 cup flour, cornstarch, baking powder, and salt. Gradually stir in beer.
Heat at least an inch of coconut oil in a large pot over medium-high heat until it registers 350°F on a deep fry thermometer. Working in batches to prevent crowding, dredge onion rings in the batter and immediately drop into the oil.
Cook onion rings, turning once, until golden, about 3 minutes total. Transfer cooked rings to the cooling rack set over the baking sheet. Keep warm in oven while frying remaining batches.