La Posta is a rustic jewel in the heart of the Mission, the kind of place where regulars claim a barstool to watch fútbol and gulp down Coronas, while mothers and children crowd around tables to consume massive plates of steaming, cheese-filled enchiladas. It's the kind of place where you can have a three-hour lunch with an old friend in the late afternoon -- there's a hearty special for only $5 -- and get tended to by a friendly waitress who immediately brings baskets of crispy tortilla chips and a pot of spicy salsa. But the down-home ambience, while a mighty fine reason to visit La Posta in the first place, isn't even the main one: This restaurant, you see, is home to the best damn mole negro in the city. A perfect balance of savory and sweet, La Posta's mole is a thick, tangy combination of chocolate, chili, garlic, and other fresh ingredients. Topping everything from enchiladas to chicken, the sauce gives platters an earthy, rich flavor, making the eatery's menu a memorable one.