Make the fried sage leaves, if using: Pour enough olive oil in a heavy skillet to cover the bottom by about 1/8 inch and heat over medium heat until the oil shimmers. Add the sage leaves in a single layer and fry until brittle but still a bright green color with no browning, 15 to 30 seconds. Transfer to a plate lined with paper towels and sprinkle with salt.

Cook the pork: Position a rack in the center of the oven and heat the oven to 375 degrees F. Season the pork tenderloin with the salt and pepper and rub it evenly with the pink peppercorns, if using.

Heat 1 tablespoon of the butter and the oil in a 10-inch ovenproof skillet or straight-sided saute pan over medium-high heat. Put the pork in the pan and sear it until golden brown on all sides, about 5 minutes total. Transfer the skillet to the oven and roast until an instant-read thermometer inserted in the center of the meat registers 140 degrees F, 10 to 15 minutes. Move the pork to a cutting board and tent loosely with foil.

Pour off and discard most of the fat left in the skillet. Set the skillet over medium-high heat and add the Marsala. Bring to a vigorous simmer, scraping the bottom of the pan with a wooden spoon to loosen any browned bits. Simmer until reduced by half, about 2 minutes. Off the heat, add the remaining 1 tablespoon butter and the chopped sage. Swirl or stir the sauce until the butter melts.

Slice the pork into 12 pieces, arrange them on a platter, and pour the hot pan sauce over the meat. Garnish with the fried sage leaves, if using.