* 1 1/2 tablespoons rich-tasting pork lard or olive or vegetable oil
* 1 2-pound boneless pork loin roast, untied if in two pieces
* 1 pound (10 to 12 medium) tomatillos, husked and rinsed
* Fresh hot green chiles to taste (roughly 3 serranos or 1 jalapeno), stemmed
* 1 medium white onion, sliced
* 3 large garlic cloves, peeled and finely chopped
* 1 or 2 large sprigs fresh epazote, plus extra for garnish
* OR 1/3 cup chopped fresh cilantro, plus a few sprigs for garnish
* Salt
* 10 small (about 1 1/4 pounds total) red-skin boiling potatoes, scrubbed and quartered
Browning the pork. In a medium-size (4- or 5-quart) Dutch oven or other heavy pan with tight-fitting lid, heat the lard or oil over medium. When quite hot, lay in the pork loin (if there is more than one piece, don’t crowd them or they’ll stew rather than brown). Brown well on one side, about 5 minutes, turn it over and brown the other side. Remove the pot from the heat and transfer the pork to a plate; set aside the Dutch oven or pan to use for the sauce making.
The sauce. Roast the tomatillos and chiles on a baking sheet 4 inches below a very hot broiler until darkly roasted, even blackened in spots, about 5 minutes. Flip them over and roast the other side — 4 or 5 minutes more will give you splotchy-black and blistered tomatillos and chiles that are soft and cooked through. Cool and transfer everything to a food processor or blender, being careful to scrape up all the delicious juice that has run out onto the baking sheet. Process until smoothly pureed.
Set the pork-browning pan over medium heat. When hot, add the onion and cook, stirring regularly, until golden, about 7 minutes. Stir in the garlic and cook a minute longer.
Raise the heat to medium-high, and, when really sizzling, add the tomatillo puree all at once. Stir until noticeably darker and very thick, 3 to 4 minutes. Add 1 1/2 cups of water and the epazote or cilantro. Taste and season with salt, usually 1 teaspoon. Stir everything thoroughly.
Braising the pork. Heat the oven to 325. Nestle the browned pork into the warm sauce, cover the pot, and set in the oven. Cook 30 minutes.
While the meat is cooking, simmer the potatoes in heavily salted water to cover until tender, about 10 minutes. Drain and set aside.
When the pork has cooked 30 minutes, nestle the cooked potatoes into the sauce around the meat, re-cover and cook about 10 minutes longer, until the pork registers about 145 on a meat or instant-read thermometer. The meat will feel rather firm (not hard) to the touch, and cutting into the center will reveal only the slightest hint of pink.
Serving the dish. With a pair of tongs and a spatula, transfer the pork to a cutting board. Let it rest there for 3 or 4 minutes while you finish the sauce: Spoon off any fat on the top of the sauce, taste the sauce and season it with additional salt if you think necessary. Spoon the sauce and potatoes onto a warm, deep serving platter.