For Stuffing:
Place dried porcini in a 2-cup measuring cup. Add boiling water to cover. Let soak for 30 minutes.
Using a slotted spoon, transfer mushrooms to a work surface. Reserve soaking liquid. Chop mushrooms; reserve.
Cook the chard in a large pot of boiling salted water for 5 minutes. Transfer to a large bowl of ice water to cool. Drain; squeeze out liquid.
Heat oil in a large skillet over medium heat. Add leeks, onions, garlic, and a pinch each of salt and pepper. Cover and cook, stirring occasionally, until vegetables are soft, about 10 minutes. Add chopped crimini mushrooms, sage, and half of chopped porcini. Cook, uncovered and stirring occasionally, until crimini are soft, about 5 minutes.
Place bread cubes in a large bowl. Add mushroom mixture with any liquid from pan and chard; stir to combine. Stir in Parmesan; season with salt and pepper. DO AHEAD: Can be made 1 day ahead. Cover and chill stuffing, remaining porcini, and soaking liquid. Add eggs and mix well to moisten bread, adding some of reserved porcini soaking liquid to moisten if necessary (leave any sediment behind).
For Roast:
Preheat oven to 325°F. Combine 6 teapoons paprika, 2 tablespoons salt, 4 teaspoons sage, 4 teaspoons pepper, and cardamom in a small bowl. Place veal breasts on a work surface and pound thickest part of veal with a meat mallet into even thickness. Rub spice mix all over. Spread 1 1/2 cups stuffing over each, leaving a 1" border on all sides. (Place remaining stuffing in a small baking dish; bake with veal during last 30 minutes of roasting). Roll veal into cylinders and tie crosswise with kitchen twine at 1" intervals.
Heat oil in a heavy pot large enough to hold both veal breasts over medium-high heat. Add veal to pot and cook until browned on all sides, 57 minutes. Transfer veal to a large plate.
Add remaining reserved porcini from stuffing, leeks, carrots, celery, and onion to pot. Add remaining 2 teaspoons paprika and 1 teaspoon sage; season with salt and pepper and stir to coat. Add wine, broth, and any remaining porcini soaking liquid. Boil for 2 minutes. Add veal. (Liquid should come halfway up sides of veal; add more broth if necessary).
Cover, transfer to oven, and cook, basting and rotating veal every hour, until very tender, 2 1/23 hours, depending on thickness of veal. Transfer veal breasts to a carving board; tent loosely with foil.
Meanwhile, spoon fat from surface of sauce. Strain sauce into a saucepan. Transfer vegetables to a blender; purée until smooth, adding some sauce as necessary. Add 2 cups puréed vegetables to sauce in pan. Simmer over medium-high heat until reduced to 4 cups, 810 minutes. Season to taste with salt and pepper. Set aside 3 cups for veal and reserve the remaining 1 cup sauce for another use.
Slice veal into 3/4"1"-thick slices and serve with sauce.
