Heat oven to 425°F. Place onion, garlic and peppers on a baking sheet lined with parchment.
Roast 20-30 minutes, or until pepper skins are blistered. Rotate peppers once or twice while cooking to make sure all sides get charred.
Remove vegetables from oven. Wrap peppers in foil or place in a a covered bowl for 10 minutes to steam, then peel skins off and remove stems and seeds.
Place peppers and onion in a blender. Squeeze garlic cloves from the peels into the blender. Add remaining ingredients, starting with 1 cup of broth.
Blend until smooth. Add more stock until you reach your desired consistency.
Pour over enchiladas, or your other favorite Tex-Mex dishes, or store according to preference.
Store 2-3 days in and airtight container in the fridge; 3-6 months in the freezer.
To can, add 1-2 tsp. of lemon or lime juice to each 1 pint jar; ladle sauce into clean sterilized jars. Place jars in a pressure canner, filling with water to cover jars with 2 inches of water. Place the lid and lock. Bring pressure up and keep pressurized for 50 minutes. Turn the stove off and allow the pressure to come down completely before opening the lid.
