Basic Tex-Mex Sauce

4 medium to large ancho chiles
2 tablespoons olive oil
6 ounces lean stew meat, cut into 1/4-inch pieces or smaller
5 cups water
1/2 onion, cut in half
2 teaspoons Mexican oregano
5 cloves garlic
1/4 cup ground cumin
1 1/2 tablespoons olive oil
1 1/2 tablespoons butter
3 tablespoons flour
1/2 cup tomato pur