Prepare the Onions:

1. Peel the onions and cut them into rings.
2. Separate the rings and set aside.

Make the Batter:

1. In a bowl, whisk together the flour, baking powder, and salt.
2. In another bowl, beat the egg and add the milk. Mix well.
3. Gradually add the dry ingredients to the wet ingredients, stirring until smooth.

Coat the Onion Rings:

1. Dip each onion ring into the batter, ensuring a thorough coating.
2. Let any excess batter drip off.

Bread Crumb Coating:

1. Roll the battered onion rings in the bread crumbs or panko for an even coating.
2. Press the crumbs onto the onion rings for better adherence.

Heat the Oil:

1. In a deep fryer or a heavy-bottomed pot, heat the vegetable oil to 350°F (175°C).

Fry the Onion Rings:

1. Carefully place the coated onion rings into the hot oil, frying only a few at a time to avoid overcrowding.
2. Fry for 2-3 minutes per side, or until golden brown.

Drain and Serve:

1. Use a slotted spoon to remove the onion rings from the oil.
2. Place them on a plate lined with paper towels to drain excess oil.
3. Serve immediately while still hot and crispy.