Preheat oven to 350°F Arrange ribs in single layer in large roasting pan. Add just enough boiling water to cover ribs. Cover pan with foil. Oven braise ribs 1 1/2 hours.
Cut bottom 2 inches from lemongrass stalk and discard upper portions. Slice lemongrass into thin rounds and place in blender.
Add to the blender 1/2 C soy sauce, sugar, sherry or sake, peanut sauce, sesame oil, garlic, and ginger and blend until almost smooth. Blend in coconut milk and the remaining 6 T soy sauce.
Cool ribs, still covered for 20 minutes. Transfer ribs to heavy duty 2 gallon resealable plastic bag; discard braising liquid. Pour marinade into bag and seal top. Turn several times to coat ribs evenly. Refrigerate overnight. Turn several times.
Preheat oven to 350°F Arrange ribs in single layer on large rimmed baking sheets. Spoon marinade from bag over ribs.
Roast uncovered until ribs are very tender, basting often with marinade about 1 1/4 hours. Adjust the time so ribs do not dry out.