Slice the onion into 7 thick rings and separate them.

In a bowl, whisk together the flour, baking powder, salt, and pepper.

In another bowl, beat the egg and then whisk in the milk to create a wet batter.

Heat vegetable oil in a deep pan or pot to about 350°F (175°C).

Dip each onion ring into the dry flour mixture, then into the wet batter, and finally back into the flour mixture, ensuring it's fully coated.

Carefully place the coated onion rings into the hot oil, frying 2-3 at a time to avoid overcrowding.

Fry for 2-3 minutes per side, or until golden brown and crispy.

Remove the onion rings with a slotted spoon and place them on a paper towel-lined plate to drain excess oil.