How to Make It
In a saucepan, bring the dates, rosemary and 4 cups of water to a boil. Simmer over moderate heat, mashing the dates with a wooden spoon, until very soft and the sauce is thick, 15 minutes. Strain, pressing on the solids; keep warm.
In a small saucepan, bring the cream to a simmer. Slowly whisk in the cheese until well blended. Transfer the sauce to a bowl, season with salt and let cool until lukewarm.
Preheat the oven to 425°. Using a sharp knife, score the duck fat in a crosshatch pattern at 1/2-inch intervals. Heat a 12-inch ovenproof nonstick skillet. Season the duck with salt and pepper and add to the skillet skin side down. Cook over moderate heat until most of the fat is rendered and the skin is deep golden and crisp, about 8 minutes. Turn the duck over and roast in the oven until medium-rare within and an instant-read thermometer inserted in the center registers 130°, about 12 minutes. Transfer the breasts to a cutting board and let stand for 10 minutes. Slice the duck crosswise 1/4 inch thick and arrange on plates.
Whisk the Piave sauce until slightly thickened, about 1 minute. Serve the duck with the date jus and the Piave sauce.