These Buttermilk Batter-Fried Onion Rings are best served the moment they come out of the fryer.
Cut onions into 1/2-inch slices, and separate into rings. Set aside.
Whisk together flour and next 4 ingredients until smooth.
Pour oil to a depth of 2 inches into a Dutch oven; heat to 375°.
Dip onion rings in batter, coating well. Fry, a few rings at a time, until golden. Drain on paper towels. Serve immediately.