In a bowl, mix the mustard, paprika, coriander, garlic powder, and salt.
Spread the rub all over the ribs and pat it into the meat.
Tear aluminum foil into rectangles and wrap each rack in the foil to create sealed parcels of meat. Arrange the wrapped racks onto a baking tray and place into the oven for 2 1/2 hours.
Take the tray out of the oven and let the packets cool a little until they are cool enough to touch with your fingers. Tear open the foil and brush each rack with barbecue sauce. Put it back into the oven, uncovered, to bake for another 5-10 minutes until the sauce becomes sticky on the ribs. Remove from oven and let rest for 10-15 minutes before cutting into portions and serving.