Remove the stems and seeds from the dried chili peppers.
Place the peppers on a baking sheet and roast them in a 350-degree Fahrenheit oven for 2-5 minutes or until fragrant. Be careful not to burn them.
Soak the peppers in hot water for 30 minutes or until cool.
In a blender, combine the peppers and 2 and ½ cups of the soaking water, garlic, cumin, and salt. Blend until smooth.
In a saucepan, stir the flour into the oil or melted shortening over medium heat until browned.
Carefully stir in the blended chili mixture and simmer uncovered for 5-10 minutes or until slightly thickened.
Add up to 1 cup of the remaining soaking water to reach your desired consistency if the sauce becomes too thick.
Pour the sauce over tamales or your favorite Mexican dish, and enjoy!
