1. Center a rack in oven and heat to 325 degrees. In a small bowl, whisk brown sugar, salt, and 1/2 teaspoon five-spice powder. Rub mixture all over ribs and wrap each rack in foil so that the seam runs along meat side of ribs. Transfer packets, seam side up, to a baking sheet and bake until ribs are tender and meatiest parts register 190 to 205 degrees, 1 1/2 to 2 hours.
2. Meanwhile, heat oil in a small saucepan over medium until shimmering. Add garlic and remaining 1/4 teaspoon five-spice powder and cook, stirring constantly, until fragrant, about 1 minute. Whisk in hoisin, vinegar, mustard, and Sriracha and bring to a gentle simmer. Reduce heat to medium-low and simmer, whisking often, until sauce is thick and glossy, about 10 minutes. Remove from heat and set aside until ready to grill.
3. When ribs are done, open a corner of each packet and carefully pour juices into a medium heatproof bowl. Skim off fat, then whisk up to 1 cup juices into sauce.
4. Heat grill to medium for at least 10 minutes, then clean and oil grates. Brush ribs all over with sauce and transfer to grill. Cook, covered, until racks are lacquered and heated through, 10 to 15 minutes, flipping and brushing with more sauce occasionally. Leave whole or slice into individual ribs, then transfer to a platter. Sprinkle with scallions and serve with more sauce on the side.
Source: Hannaford fresh Magazine, May - June 2020