In a large bowl, combine flour, baking powder and salt. Dip the onion slices into the flour mixture, until coated, and set aside. Whisk 1 egg and milk into the flour mixture, using a fork. Dip the floured rings into the batter to coat. Allow excess to drip off of the onion rings for a moment. Pour 3/4 cup bread crumbs into a shallow bowl. Coat the onion rings and set aside. In a large bowl, mix together beef, 1/4 cup bread crumb and egg. Shape into patties. Grill the patties over medium high for 8-10 minutes per side, or to desired doneness. Meanwhile, preheat deep fryer for 365 degrees. Deep fry the onion rings for 2-3 minutes, until golden brown. Season the onion rings with seasoned salt. Arrange burger using favorite condiments. Top with onion rings.