Achiote Paste

Achiote paste, favored in Yucatán and Oaxacan cuisine, is made from the slightly bitter, earthy flavored, red annatto seeds, mixed with other spices and ground into a paste. Achiote is a distinctly colored and flavored mainstay of the Mexican kitchen.

A typical preparation mixes:
1/4 cup annatto seeds
1 tablespoon coriander seeds
1 tablespoon oregano
1 teaspoon cumin seeds
1 teaspoon black peppercorns
2 whole cloves
1 teaspoon salt
5 cloves of garlic, peeled
1/2 cup bitter orange juice (Seville) or 1/3 cup white vinegar

Grind the spices (annatto, coriander, cumin, peppercorns, oregano and cloves) in a spice mill or with a mortar and pestle. Blend the ground spices with the salt, garlic and the bitter orange juice until it is smooth. Rub the mixture onto chicken, pork or fish and let it marinate for 4–6 hours then cook as usual. Or use the achiote as an ingredient in another dish.

The paste is dissolved in either lemon juice, water, oil or vinegar to create a marinade, and marinated or rubbed directly upon meat. The meat is then grilled, baked, barbecued or broiled. Sometimes it is added to corn dough to create a zesty flavor and color in empanadas and red tamales.   

Recipe and information from Wikipedia