Preheat oven to 350. Mix hoisin sauce, ginger, 1 teaspoon chinese 5 spice & 1/2 tsp red pepper flakes. Reserve 1/2 cup of the mixture until ribs are done.
Combine broth, soy sauce and garlic in a roasting pan (with a lid). Remove membranes from ribs and cut between bones to separate ribs and cut each rack in half. Sprinkle meaty side of ribs with remaining chinese 5 spice. Arrange ribs in roasting pan and overlap as needed. Cover and bake for 45 minutes.
Remove roasting pan from over, turn and baste ribs with remaining sauce and bake, covered, for an additional 45 minutes to 1 hour and 15 minutes.
Remove ribs and arrange on platter. Sprinkle with seeds and onion.