• Adjust the oven rack to the middle position and heat the oven to 300°F. Line a rimmed baking sheet with aluminum foil and set a wire rack on the sheet. Spray the rack with non- stick spray.

For the Rub

• Combine the brown sugar, paprika, salt, garlic powder, black pepper, and piment d’Espelette in a small bowl.
• Rub each set of baby back ribs with 1/2 cup of the sweet heat rub. Set aside to come to room temperature, 30 minutes.(This step can be done a day ahead for deeper flavor: Rub the ribs with the rub and place in a resealable plastic container, or wrap in plastic wrap. If you use plastic wrap, make sure to place the wrapped ribs on a rimmed baking sheet to catch any seeping liquid due to the salt in the rub. Refrigerate to marinate overnight.)

For the Tangy BBQ Sauce

• Heat the oil in a saucepan over medium heat. Add the onion and simmer until soft, 5 to 7 minutes. Add the ketchup. Pour the vinegar into the ketchup bottle and shake to loosen all the ketchup from the sides. Pour the vinegar from the bottle into the saucepan and add the Worcestershire sauce, mustard, brown sugar, lemon juice, hot sauce, and pepper.
• Bring to a boil, decrease the heat to low, and simmer until the flavors have smoothed and mellowed, at least 10 minutes and up to 30 minutes. Taste and adjust the seasoning with salt and pepper. Store in an airtight container in the refrigerator. The sauce will last for months.

To Cook the Ribs

• Place the rubbed ribs side by side on the prepared baking sheet. Transfer to the oven and roast until the ribs are done and a knife slides easily into the thickest part of the rib meat, 2 hours.
• Remove from the oven and let the ribs rest, covered loosely in aluminum foil, for about 10 minutes, and then cut between the bones to separate the individual ribs.
• Serve immediately with the barbecue sauce for dipping.