In a medium saucepan over medium-high heat preheat the oil. Add the onion and cook until the edges of the onion start to brown, about 3-5 minutes.
Add the garlic, chili powder, cumin, salt, and oregano and cook until fragrant, about 30 seconds.
Stir in the tomato sauce and chicken broth. Bring the mixture to a simmer and keep at a simmer and cook for 10 minutes, stirring occasionally.
Remove the sauce from the heat. Using an immersion blender, blend until smooth, about 2 minutes. If you don't have an immersion/stick blender, you can use a blender. Just make sure you hold the lid on *VERY* tight, trust me I know from experience!
Keep in an air-tight container in the refrigerator for up to 1 week.
This recipe makes about 3 cups of homemade Enchilada Sauce.