Preheat the oven to 450°F.

In a food processor, combine rosemary leaves, garlic, oil, vinegar, salt, and pepper. Pulse to make a course, wet paste, scraping down the bowl as necessary.

Spread 3/4 of the paste on all sides of the pork roast.

Place roast, fat side up, in a shallow roasting pan. The pan should be large enough to hold the roast with 3 inches of room around all sides.

Place the pork in the oven and roast for 15 minutes.

Meanwhile, in a large bowl, combine potatoes and remaining paste.

Add potato mixture to the roasting pan, arranging potatoes around the roast. Reduce the temperature to 350°F and continue roasting for 40–45 minutes, tossing potatoes halfway through.

The pork roast is fully cooked when the internal temperature reaches 145°F, and the potatoes are fully cooked when tender. If the roast is done before the potatoes, transfer it to a cutting board and continue roasting the potatoes until done.

Remove the roast from the oven and let it rest for 10 minutes.

Slice the roast and arrange on a platter. Surround with potatoes and serve.