Heat the oil in a sauce pan and whisk in the flour. Cook for 1 minute, then pour in the chicken broth.
Continue whisking over medium heat until it has thickened slightly.
Add the remaining ingredients and simmer for 5 minutes or until the sauce is the desired thickness you wish.
Let cool completely before storing in the refrigerator.
This recipe makes about 5 cups of enchilada sauce.
Roux The Day. The order in which you add the ingredients to the sauce is important because this enchilada sauce starts with a roux made by whisking together oil and flour. Once that paste-like roux is made, then whisk in the broth until thickened. Only after the sauce is thickened will the remaining ingredients be added and then the sauce will simmer until it has the flavor and consistency that you like.
Consistency. If the sauce is too thin, then let it simmer a little longer in order to thicken. If the enchilada sauce is too thick, you can thin it out by adding a little chicken broth to it.
Adjust Spice Level. In this recipe, the chili powder and optional cayenne pepper will add spicy heat. If you want it less spicy, first I recommend tasting the sauce before adding either chili powder or cayenne. That way you can determine if, and how much of the chili powder to add. For less spicy heat, use less chili powder. For more spicy heat, add more chili powder. To make it even spicier, add cayenne pepper. Add a little at a time until you get it to the heat level that you like.
Reduce Acidity. To reduce the acidity of the tomatoes try adding a teaspoon or two of sugar. This will help to balance out the flavor of the sauce.
Make-Ahead. Make the enchilada sauce a day ahead and refrigerate until about 30 minutes before cooking. This will make for an even more flavorful enchilada sauce because it gives the flavors time to more fully develop.