Divide the veg between a few large pans (keeping the beets separate), cover with boiling salted water and parboil for 10 to 15 minutes, or until starting to soften. Drain the veg in a large colander and leave for a couple of minutes to steam dry. Give the colander a good shake to chuff up the edges, then tip into your largest roasting tray. Drizzle with the duck fat, pick over the rosemary leaves, season with salt and pepper, then toss to coat. Push the veg into a single layer, then cook at 220°C/425°F/gas 7 for around 40 minutes, or until golden, crispy and delicious, turning halfway through for even cooking. Serve with the roast duck and the Marsala gravy.