2Toast the chiles on a skillet over medium heat for 30 seconds to 1 minute on each side, but do not allow them to scorch. Tear the chiles into pieces, place them in a bowl, cover them with boiling water, and allow them to rehydrate and soften for 15 minutes. Drain the chiles and place them in a blender.
3Add the orange juice and lime juice and blend for 1 minute. Strain the mixture through the fine blade of a food mill, then add the grenadine, tequila, salt, thyme and onion, and reserve.
4Salt and pepper the pork. In a Dutch oven or heavy baking dish, heat oil over medium high heat until it is very hot but not quite smoking. Add pork and sear it, turning as necessary, until it is golden brown on all sides, about 4 minutes. Remove the pork to a plate and the pot from the heat and allow it to cool, briefly.
5Add the chile mixture, stirring well to incorporate any caramelized pieces of pork and juices from the bottom of the pot. Put the pork back in the pot, fat side up, replace it on the burner and heat until the sauce just begins to bubble lightly, but do not bring it to a complete boil.
6Place the pot in the preheated oven and bake, uncovered, until pork reaches an internal temperature of between 145 and 150 degrees, (about 30 minutes per pound for a roast with two loins tied together, or a total of about 1 hour for a single loin) spooning some of the sauce over it every 15 minutes.
7Remove the pork from the pot, and allow it to rest for 5 minutes, then slice it into servings. While the meat is resting, reduce the sauce if it is too thin.
8Spoon some sauce on each of 4 serving plates, and top with a slice of pork. Mexican-style white rice and sautéed nopalitos or squash go well with this dish.