Step 1

Heat the olive oil in a medium saucepan over high heat. Add the onion, garlic, and pinch salt, and cook, stirring often, until the onion is softened.

Step 2

Add the remaining ingredients. Use an immersion blender to blend ingredients together until smooth.

Step 3

Bring to a simmer, reduce heat to medium-low, and simmer the ranchero sauce gently, stirring regularly, for 30 minutes to concentrate and blend flavors.

Step 4

Taste for seasoning and add the butter. Yields a little over 4 cups sauce.