Preheat oven to 375 degrees F. With a pastry brush, spread the mustard all over both sides of the ribs. Generously sprinkle the rub all over both sides of the ribs.
Place ribs in the middle of a double thickness of heavy foil cut 6 inches longer than the ribs. Wrap ribs in the foil. Bake for 1 1/2 to 2 hours or until tender (the two middle bones of the rack should start to pull apart easily).
Remove ribs to a tray (discard liquid in foil packet). Spread the sauce all over both sides of the ribs. Grill on the rack of a covered grill directly over medium heat for 15 minutes, brushing with additional sauce every 5 minutes, turning once. Adjust heat as necessary to prevent burning.
Place celery seeds, cumin seeds, mustard seeds, and coriander seeds in a spice grinder and grind until fine. Mix together with remaining ingredients.
Whisk all ingredients together in a large saucepan and bring to a simmer. Simmer, covered, for 10 minutes, stirring occasionally. Cool to room temperature. Cover and chill up to 2 weeks.