Baby back ribs with spiced apple-cider mop

For the mop:
2 cups apple cider
1/4 cup minced shallots
1 tablespoon minced jalapeño pepper, seeds removed
1/4 cup ketchup
2 tablespoons white wine vinegar
2 tablespoons tomato paste
1 tablespoon dark brown sugar
1/4 teaspoon kosher salt
1/4 teaspoon freshly ground black pepper
2 to 3 slabs baby back pork ribs, about 4 pounds
Kosher salt
Freshly ground black pepper

1. To make the mop: In a small saucepan combine the apple cider, shallots, and jalapeño. Bring to a boil and cook over medium-high heat until about 1 cup of the liquid remains, 15 to 20 minutes. Add the remaining mop ingredients, bring to a boil, and remove from the heat. (The mop may be made ahead and refrigerated until ready to use.)
2. Allow the ribs to stand at room temperature for 20 to 30 minutes before grilling. Season with salt and pepper. Grill, rib side down, over Indirect Medium heat until the meat is very tender and has pulled back from the ends of the bones, 1-1/2 to 2 hours. Baste the ribs frequently with the mop throughout grilling time, but stop basting during the last 10 minutes. Remove from the grill and allow to rest for 5 to 10 minutes before slicing into individual ribs. Serve warm.