Add all dry ingredients to a small bowl and whisk to combine.
Coat both sides of the rib racks with mustard.
Use your hands to press ¼ cup of the dry seasoning to both sides of the rib racks. Reserve the rest of the seasoning for later use.
Place the ribs on a medium-high grill and sear until both sides are charred (8-10 minutes on each side).
Reduce the grill heat to low. Wrap the ribs in foil and shift the ribs away from the direct flames. Allow to cook for 2.5 hours.
Remove ribs from the grill and rest for 15 minutes before serving.