If using dried chipotle, soak them in hot water for 20-30 minutes until soft. Remove stems and seeds.
In a pan, heat olive oil. Sauté chopped onions until soft, then add garlic.
Stir in tomato paste and cook for 1-2 minutes for richer flavor.
In a blender, combine softened chipotles, sautéed mix and water or broth.
Add salt and a splash of vinegar for brightness. Blend everything until smooth.
Pour the sauce back into the pan and simmer for 10-15 minutes to deepen the flavor.
Let it cool, then store in a jar. Keeps well in the fridge for up to a week.