The best restaurant hamburger I ever had was at my dad's joint he had from 1965-75, Kelly's Inn, on E 17th and Grand in Des Moines. Cast iron grill, great beef, toasted buns to have that crisp crunch and nice onion slice and condiments. It was a smaller place that was packed from 6 AM to 2AM for 20 hours with workers from 3 shifts, Statehouse workers for lunch, etc. My dad also cashed payroll checks which would bring in the crowds on Thursdays and Fridays.
B-Bops in Des Moines has a great hamburger/cheeseburger. Our daughter lives in Seattle and has had Five Guys but she says B-Bops is better. B-Bops is open flame cooked burgers which is also like "Iowa's The Best Burger Cafe" around Kellogg along I-80 about mile marker 173 just west of Grinnell. Very very good.