Combine sugar, 5-spice powder and garlic. Rub mixture well into each rib. Cover and marinate overnight in refrigerator.
Remove ribs from refrigerator and allow to sit at room temperature for at least 30 minutes, to 45 minutes.
For the sauce, heat oil over medium-low heat and add onions; cook slowly until they are caramelized. Add garlic and stir to blend. Add remaining sauce ingredients and bring to a simmer. Cook 5 minutes and remove from heat.
Preheat oven to 325°F
In a large, heavy skillet or Dutch oven, sear each rib until brown. The sugar in the rub will make the ribs brown quickly, and you may need to change pans if the build-up in bottom of pan gets to thick. After all ribs are seared, place them side by side, in single layer, in a deep roasting pan. Add sauce.
Cover pan with foil and cook in oven for 2 1/2 hours, or until tender.
Remove ribs from pan and keep them warm. Transfer pan drippings and sauce to a blender and puree (be very careful when blending hot liquids). Pour into a saucepan and reheat for serving.
Serve ribs with sauce and garnish with chopped peanuts.