2tablespoonsolive oil or rice bran oil plus more for the cooking surface
Salt and freshly ground black pepper
4poundssteak(loin, round, or flat)
To make the marinade:
To the bowl of a food processor or blender, add red onion, garlic, adobo sauce, ancho chile powder, olive oil, cumin, dried oregano, 1 tablespoon salt, and 1 teaspoon pepper.
Blend until smooth. Pour into a measuring cup and add water to reach 1 cup.
Place the steak in a large zipper-top plastic and add 1 cup marinade. Refrigerate overnight if desired. Let beef sit in the marinade for at least 30 minutes at room temperature before grilling.
To make the steak:
Heat 2 tablespoons oil in a large skillet until shimmering (or preheat a grill over medium high heat). Add steak to the pan and cook, turning occasionally, until the temperature reaches 135 degrees for rare or 145 degrees for medium rare. Depending on the size of your skillet, you can cook the steak in batches.
Remove to a cutting board and tent with foil for 10 minutes. Chop into small pieces. Season to taste with salt. Serve on tortillas or in bowls with additional toppings as desired.
To make the marinade with dried ancho chiles:
Remove stems and seeds from 1 ounce (2-3 small) dried chiles (wearing gloves is recommended). In a dry skillet over medium-low heat, toast the chiles until fragrant but not smoking, about 5 minutes.
Transfer to a medium bowl and add 4 cups (1 quart) water. Microwave on HIGH for 6 minutes. Drain well. Split open each softened ancho chile and rinse the inside to remove the stem and all seeds (wearing gloves is recommended).
Add to the food processor with the other marinade ingredients.