For the onion rings, fill a countertop fryer with oil or pour a few inches of oil into a large Dutch oven. Heat oil to 365° F. (The oil is ready for frying when a 1-inch cube of white bread cooks to golden brown in 40 seconds.) Combine buttermilk and sour cream in a bowl and add the onion rings; soak for a few minutes. On a plate, toss the flour with the chives; season generously with salt and pepper. Dip the onion rings in the seasoned powder, then again in the buttermilk, and again in the flour. Fry 1 or 2 rings at a time in the hot oil, turning once, until deep golden, about 4 minutes. Transfer to a rack to cool.