Place the ribs in a large pot of cold water. Bring to a boil and simmer for 30 minutes; drain. Pat the ribs dry with paper towels and return to the dry pot.
Combine 6 T. of the soy sauce, the sugar, hoisin sauce, rice wine, ginger, 2 cloves of the minced garlic, and the chili. Pour over the ribs and turn to coat. Marinate at room temperature for 30 minutes.
Meanwhile, toss the sweet potatoes and the 3 remaining cloves of garlic in the vegetable oil with the remaining soy sauce. Place in a single layer in a large roasting pan lined with aluminum foil or parchment paper. Roast for 15 minutes.
Place the ribs on top of the sweet potatoes, reserving any extra marinade. Return to oven and roast for 45 minutes or until dark and sticky. Baste with the extra marinade periodically.
Remove ribs from the pan, set aside, and keep warm. In a bowl, mash the sweet potatoes, garlic, butter and lemon juice. Serve with the ribs on a bed of baby spinach.