About one hour before you plan to start grilling, make the rub: In a small bowl, combine the brown sugar, salt, chili powder, lemon peel, paprika, onion powder, cayenne and pepper. Pat the ribs dry with paper towels, then sprinkle both sides of each rack with the rub. Set aside at room temperature for one hour.
Preheat the grill for indirect cooking at 250 to 300 degrees F. Add the drained wood chips, if using.
Place the ribs, meaty side up, over a drip pan, close the grill, and cook for 2 hours, adding about 12 coals to a charcoal grill every 45 minutes or so to maintain the heat.
Meanwhile, make the sauce: In a medium saucepan over medium heat, combine the jam, salsa, white sugar, onion powder, vinegar, liquid smoke and cayenne and bring to a boil. Reduce to a simmer and cook 15 minutes, stirring frequently, until lightly thickened. Set aside to cool to room temperature, then refrigerate.
Continue to cook the ribs until they’re so tender the rack will easily break when bent with tongs, 1 to 2 more hours, spraying on both sides with the tamarind juice every 20 to 30 minutes. Brush the ribs on both sides with the sauce and continue to cook for about 5 minutes, until the sauce is set. Remove from the grill and let stand for 5 minutes.
Cut the racks into 3- or 4-rib sections and serve. Pass any remaining sauce at the table.
* Look for liquid smoke in the barbecue sauce section of your supermarket. Look for tamarind juice in the Asian or Hispanic foods section. If necessary, you can substitute tamarind soda or even apple juice.
Serving Suggestions: Make these smoky-sweet ribs your own by using different flavors of jam for the barbecue sauce—cherry, plum, and currant would all be good. Alongside, serve grilled corn and a tomato-cilantro salad.