In a small bowl, combine the brown sugar, salt, juniper berries, bay leaf, peppercorns, and coriander seeds. Mix well. Place about one-third of this mixture in the bottom of the loaf pan. Lay one magnet, fat side up, on the salt and sugar mixture. Cover with another third of the mixture and lay the second magret on top of that. Top with the remaining salt and sugar mixture, being sure that the duck breasts are well coated. Cover with plastic wrap and refrigerate for 6 to 8 days, until the meat cured. The prosciutto is done when the duck breasts are firm to the touch, with the stiff texture and dark color of cooked meat. The fat should be a creamy, off white color. Completely wipe off the seasoning and wrap in plastic. Store in the refrigerator until ready to use.

Note: Magret is a French term that refers specifically to the breast of a duck that produced foie gras. You can make duck prosciutto from regular duck breasts, but the meat won't be as flavorful