Crack the black pepper and coriander seed in a coffee grinder, separately. If processed simultaneously, the coriander will become too fine.
Drain off the water from the brisket. Pat dry with paper towels. Smear it with dark molasses, coating thoroughly. Sprinkle on a small quantity of garlic powder. Sprinkle on roughly equal amounts of cracked black pepper and coriander to completely envelop the brisket. Firmly press these two spices into the flesh. Finish off with a good dusting of paprika.
Prepare a smoker. Use hickory chunks or chips as the flavoring medium. Adjust heat to 225 degrees F. Place the meat into the smoker. Smoke for 5-6 hours or until the internal temperature registers 165 F.
Find or purchase a pressure cooker and a rack that will fit into it. Insert the rack into the body of the device. Fill the pressure cooker with cold water up to the bottom level of the rack. Place the pastrami on the rack, lock the lid, turn the flame to high and allow the device to come up to pressure (15psi is the standard). When the cooker starts to spit steamy water, turn the flame down to about medium - where the vapor stream is slow and constant. Pressure steam the pastrami for 30 minutes. Cut off the heat.
Allow the cooker to depressurize naturally. This will take approximately 10 minutes. Unlock the lid and remove the pastrami. With a razor-sharp butchering knife, carve the pastrami into thin (but not too thin) slices. Serve on rye bread - slathered with deli mustard on both sides.