One 4 1/2- to 5-pound pork shoulder butt, excess fat trimmed
6 garlic cloves, thinly sliced
2 tablespoons extra-virgin olive oil
2 tablespoons pure ancho chile powder
1 tablespoon ground cumin
Preheat the oven to 425°. Using a paring knife, make deep, narrow slits all over the meat and fill each slit with a slice of garlic. Transfer the roast to a sturdy roasting pan.
In a small bowl, make a paste with the olive oil, ancho powder, cumin and 1 tablespoon of kosher salt. Rub the paste all over the pork and roast for 1 hour. Reduce the oven temperature to 375°. Cover the pork with foil and roast for about 1 hour and 15 minutes longer, until an instant-read thermometer inserted in the thickest part of the meat registers 150°.
Transfer the roast to a cutting board and let rest for 10 minutes. Carve the pork roast across the grain 1/3-inch thick and serve.