For the barbecue sauce: Heat the oil in a medium saucepan over medium heat. Add the garlic and saute until soft, about 3 to 5 minutes. Add the espresso, vinegar, ketchup, honey, soy sauce, hoisin, and sriracha, and a grind or two of black pepper and whisk to combine. Bring to a boil and then reduce to a simmer, stirring occasionally, until the sauce thickens, about 30 minutes. Remove from heat and let cool. You should wind up with about 2 cups of sauce. NOTE: Sauce can be made up to a week in advance and stored in the refrigerator in an airtight container.
For the ribs: Preheat the oven to 275 degrees F. Remove the thin membrane on the bone side of the ribs. Place the ribs on a baking sheet lined with aluminum foil and generously season both sides with kosher salt and black pepper. Bake for 2 1/2 half hours then remove from the oven and let cool.
When the ribs are cool enough to handle, cut each rack in half and place in a resealable plastic bag. Pour half the barbecue sauce into a measuring cup and thin with a a tablespoon or two of water and then divide it between the two bags, making sure the ribs are coated evenly on all sides. Place the bags in the refrigerator to marinate at least overnight but for up to two days. Turn the bags a few times so they marinate evenly.
Preheat oven to 350 degrees F and remove ribs from refrigerator and let come to room temperature. Place the ribs on a baking sheet lined in heavy-duty aluminum foil and bake for 30 to 45 minutes brushing them with some of the sauce every 10 minutes, until they are heated through and glazed.
(Alternately, you could grill the ribs over a charcoal or gas barbecue until hot, glazing them with sauce on each side).
Cut the racks into individual ribs and serve with the reserved sauce.