Boil ribs 1/2 hour in salted water with 3 cloves garlic and 3 leaves oregano.
To make the recado, grind the annatto seeds with a molcajete. Add remaining spices and garlic and grind thoroughly, using sour orange juice to make a paste.
Rub the recado over the ribs, and grill until done.
For the sauce: The tomatoes can be roasted over the grill about 10 minutes, over an open fire, or in a comal or frying pan. Roast the onion and garlic.
Mix the spice-blend ingredients with the tomatoes in a blender of molcajete. Slice the onions and serve on the side with the garlic and tomato sauce.