2. In a small bowl, combine flour, baking powder, and salt.
3. Dip the onion rings into the flour mixture until they are all coated; set aside.
4. Whisk the milk and egg together in a medium bowl. Dip the floured rings into the batter to coat, then place on a wire rack to drain until the batter stops dripping.
5. Spread the breadcrumbs out on a plate or shallow dish. Place rings one at a time into the crumbs, and scoop the crumbs up over the ring to coat. Give it a hard tap as you remove it from the crumbs. The coating should cling very well. Repeat with remaining rings.
6. Deep fry the rings a few at a time for 2 to 3 minutes, or until golden brown. Remove to paper towels to drain. Season with salt, and serve.
Notes:
For extra crispiness, double dip the onion rings in the batter and breadcrumbs.