1 teaspoon sea salt
1/4 teaspoon freshly ground pepper
1 teaspoon Dijon mustard
1 beef filet (rib eye), about 3 pounds
2 chiles anchos, seeds and membranes removed
5 chiles guajillos, seeds and membranes removed
1 cup water
2 cloves garlic
1/4 small onion
2 black peppercorns
1/4 teaspoon each dried marjoram and oregano
1/4 teaspoon cumin
1 tomato, roasted and peeled
2-1/2 tablespoons butter
1 teaspoon red wine vinegar

Mix salt, pepper and mustard together and rub into the filet. Place in a shallow dish and let stand for 30 minutes. Meanwhile, in an iron skillet, toast the chiles. Soak in hot water to cover for 20 minutes, then drain, discarding the soaking water. Transfer to a blender, add water and purée.
Add garlic, onion, peppercorns, marjoram, oregano and cumin and purée again. Set aside. Purée tomato and set aside.
Melt butter in a small saucepan, add chile purée and cook over high heat for 5 minutes, stirring constantly. Add vinegar; stir and cook over medium heat for 25 minutes or till the sauce thickens.
Cover the filet with the sauce and marinate for 30 minutes to an hour.

Prepare grill for medium heat. Place filet, still coated with chile marinade, on the grill. Turn often so that the meat does not burn. The filet will be done in about 25 minutes—less if you prefer it rare.
Alternately, the filet can be placed in a baking dish and roasted in an oven preheated to 400°F for 20-30 minutes.