(Optional) Remove the membrane, then slice racks into individual ribs and place in a large bowl or on a baking sheet.
Coat ribs with mustard, then season generously with rub.
Smoke at 275°F for about 1.5 hours, spritzing with diluted apple juice at the 1 hour mark.
At 175°F internal, move ribs to a foil pan. Add butter, brown sugar, honey, BBQ sauce, and bourbon if using. Toss to coat and cover tightly with foil.
Return to smoker until ribs reach 205°F and are tender, about 1 more hour.
Uncover, toss in sauce, and let set for 5–10 minutes before serving sticky and smoky.
