Peel the onion and cut into 1/4 inch (5 mm) slices.
Separate into rings and combine with the milk in a bowl. Soak for 1/2 hour.
Combine the flour with the salt, pepper, and paprika.
Heat the vegetable oil to 375F (190C).
Dredge the onion rings a few at a time in the flour mixture and carefully drop into the hot oil.
A long handled fork is useful for transferring the rings from the flour to the oil.
Fry until golden brown on both sides, about 2 minutes, turning the rings over as necessary.
Drain on paper towels, and keep warm in a moderate oven if not serving immediately.