Food Network offers a recipe for ranchero sauce from Lone Star Taco Bar in Allston, Massachusetts. The recipe calls for ingredients such as peppers. chiles, onions, tomatoes and garlic. It takes about one hour and 20 minutes to prepare.
Roast a green bell pepper, a red bell pepper and a poblano pepper under a gas broiler until it is well charred. Allow it to cool, remove the stems and seeds, coarsely chop the peppers and reserve them for later. Finely grind a dried guajillo chile and a dried pasilla chile with a mortar and pestle or spice grinder and set them aside.
Set a large saucepan over medium heat with 3 tablespoons of olive oil. Add three coarsely chopped medium Spanish onions and cook covered for about four minutes.
Add the ground dried chili and six to eight sliced garlic cloves along with 2 teaspoons each of ground cumin and chili powder, 1 teaspoon of dried Mexican oregano, 1/2 teaspoon of dried thyme, 1 teaspoon of ground black pepper and 1 tablespoon of kosher salt. Stir for about four minutes until it is fragrant.
Add two 28-ounce cans of chopped tomatoes, two 6-ounce cans of chopped green chiles and 1 tablespoon of sugar. Allow it to reach a simmer, then turn the heat to medium-low and cook for about 30 to 40 minutes until the vegetables become soft. Taste and adjust the seasonings if necessary.