If you prefer a milder sauce, remove the chipotle pepper before pureeing the tomato mixture.
Sauté onion in hot olive oil in a large saucepan over medium-high heat 5 minutes or until softened; add garlic, and sauté 1 minute. Stir in tomatoes and next 7 ingredients. Bring to a boil; reduce heat, and simmer, stirring occasionally, 25 minutes. Remove from heat, and cool slightly.
Remove chipotle pepper, if desired. Process tomato mixture in a food processor or blender until smooth. Cover and chill at least 8 hours. Serve at room temperature with tortilla chips.