Be sure to have all of the ingredients measured out and near the stove. This sauce comes together very quickly.
Heat the oil in a small saucepan over medium heat. Add the flour and whisk together for a few seconds. Whisk in the chili powder, garlic powder, cumin, salt and pepper. Whisk in the tomato paste. The mixture will darken a bit, cook a minute until fragrant.
Gradually add in the stock, whisking the entire time. Increase the heat to medium-high, bring the sauce to a boil and then to a simmer. Mix in the vinegar. Cook 5-7 minutes. Whisk often to remove lumps and to make a smooth sauce. Sauce will appear thin at first and will thicken as it cooks. Add ground red pepper now to taste if you want a spicy sauce. Test the thickness with a spoon. It will continue to thicken as it cools.
Transfer the sauce to a heat proof container to cool or use immediately for enchiladas. Enchilada sauce can be refrigerated and used within 5 days or you can freeze it for up to 3 months.