For the sauce:
Crack open the tamarind pods.
Peel the shells and fibers.
Put fruit in 2 cups of water in a large stock pot.
Cover and bring to a boil.
Reduce heat and simmer for 5 minutes.
Remove from heat and let cool. (about 20 minutes)
Push the pulp through the strainer with the back of a spoon.
Strain, discarding the seeds and any fibers.
Set mixture aside.
In a large saucepan, sauté onion.
Add tamarind pulp and the rest of the ingredients.
Bring to a gentle simmer then reduce the heat to low.
Cook for 15 minutes, stirring occasionally.
Add mixture to a blender.
Blend until smooth.
Set aside until ready to use, or store for 2 weeks in the fridge.
For the Ribs:
Preheat oven to 325 degrees F.
Wrap room-temperature ribs in aluminum foil.
Cook for 2 hours for baby back ribs, or 3 hours for spare ribs.
Preheat grill to medium-high heat.
Grill ribs for 7-10 minutes on each side, basting with BBQ sauce.
Remove and serve.