Preheat the oven to 350 degrees F (189 degrees C) or up to 370 degrees F (188 degrees C). Remove membrane from the back of the slab.
Drizzle 1 tablespoon liquid smoke on one side of the slab; massage into the meat. Flip over; massage remaining 1 tablespoon liquid smoke into the other side of the slab.
Sprinkle 1 tablespoons BBQ rub on one side of the slab (or more to taste); rub in thoroughly. Flip over; massage 1 tablespoon BBQ rub into the other side (or more to taste). Sprinkle 1 tablespoon garlic powder over each side of the slab.
Place 2 tablespoon butter on the meaty side of the slab. Wrap the slab, meaty side up, completely in foil; place on a flat pan.
Bake in the preheated oven for 1 hour. Remove from the oven and flip the slab over, bony side up. Bake for 30 minutes.
Melt remaining 2 tablespoons butter; stir remaining 1 tablespoon BBQ rub into melted butter.
Remove slab from the oven and turn back over to the meaty side. Brush meaty side with half the butter-rub mixture. Leave slab in the foil but do not cover the slab.
Bake uncovered for 30 minutes more.
Remove from the oven; brush with remaining butter-rub mixture. Allow to sit for a few minutes before cutting.