Step 1In a heavy-bottom 4-quart pot, combine the onion, garlic, lemon zest and bourbon. Bring the bourbon to a simmer over medium-high heat, then reduce the heat to maintain a simmer and continue to cook until the onion is translucent, about 10 minutes.
Step 2Stir in the lemon juice, pepper, chile powder, mustard, onion powder, salt, tomato paste, ketchup, vinegar, pineapple juice, liquid smoke, Worcestershire sauce, brown sugar, molasses, Tabasco and bitters and continue to gently simmer for 30 minutes. Stir frequently, making sure to scrape the bottom of the pot to prevent burning.
Step 3Remove from heat and puree the sauce until fairly smooth, using an immersion blender or blending in stages in a stand blender. Place the sauce in a nonreactive container and set aside until it comes to room temperature, then cover and refrigerate until needed. Warm the sauce before using.
Step 1Heat the oven to 250 degrees.
Step 2Peel the tough membrane lining the underside of the spareribs, then rinse the ribs, pat dry and place in a large roasting pan.
Step 3Evenly coat the racks on both sides with the salt, several grinds of pepper and the garlic. Set the racks aside while you make the rub.
Step 4In a medium bowl, combine the mustard, sugar, chile powder, onion powder and Tabasco to form a thick paste. Stir in the pecans until combined; this will form a sticky wet rub.
Step 5Rub the pecan mixture evenly over the rib racks on both sides to coat. Pour the beer into the roasting pan, then cover tightly with foil.
Step 6Place the ribs in the oven and cook until the meat is tender and curled away from the ends of the ribs (you should see about one-half inch of bone at the end of each rib), about 2 1/2 hours.
Step 7Remove the foil from the pan and mop the ribs with a generous coating of barbecue sauce. Cook the ribs an additional 30 minutes to allow the barbecue sauce to thicken and form a "crust" on top of the ribs. Remove from heat and allow the ribs to cool slightly. Slice and serve immediately with additional barbecue sauce on the side.