How to Make It
Squeeze any excess water from the chopped spinach. In a medium bowl, mix the spinach with the Parmesan cheese, minced garlic and 2 tablespoons of the extra-virgin olive oil. Season with salt and pepper.
Preheat the oven to 400°. Set the pork loins on a work surface, opening them like a book, with the cut side up. Season the inside of the pork loins generously with salt and pepper. Cover the pork loins with a single layer of overlapping prosciutto slices; spoon the spinach filling into the center of the pork loins. Shape the filling into a thin log that runs along the center of each loin. Roll up the pork loins and tie them with kitchen twine at 1 1/2-inch intervals. Season the pork loins generously with salt and freshly ground pepper.
Heat the remaining 1 tablespoon of extra-virgin olive oil in a very large ovenproof skillet until shimmering. Add the pork loins and cook over moderately high heat until they are browned all over, about 10 minutes. Transfer the pork loins to a large platter.
Pour off any fat from the skillet and return it to high heat. Add half of the chicken stock and bring to a boil, scraping up any browned bits from the bottom of the pan. Return the pork loins to the skillet and roast them in the oven for 40 to 45 minutes, or until an instant-read thermometer inserted in the thickest part of the meat registers 145°. Transfer the pork loins to a large cutting board, cover loosely with foil and let stand for 15 minutes.
Pour the juices from the skillet into a small saucepan and skim off the fat. Add the remaining 3/4 cup of chicken stock to the skillet and set it over high heat. Add the wine, scrape up any browned bits from the bottom of the skillet and boil until reduced to a few tablespoons. Add the pan juices to the saucepan and bring to a boil. Whisk in the flour slurry and simmer until slightly thickened. Season with salt and pepper.
Untie the pork loins and carve the meat into 1/2-inch-thick slices. Arrange the slices on plates, drizzle with the pan sauce and serve.