Preheat the oven to 325°F.

Rinse the pork shoulder and pat dry. Using a paring knife, make several ½-inch-deep incisions on both sides of the meat. Mix the juice, jalapeños, thyme, garlic, salt, pepper, and oil, either by hand or by pulsing in a food processor until just mixed. Rub the meat with the mixture, being sure to massage some down into the incisions.

Place the meat in a roasting pan fat side up, cover with foil, and roast for 3-4 hours, or until the meat is fork-tender. Cool, remove it from the pan, then shred or slice the pork as desired. After the meat has been removed, add a little water or broth to the roasting pan and stir to dissolve any brown bits, then strain the juices and pour them back over the sliced or shredded meat.