Place the bacon in a cold, 10-inch, heavy sauté pan and heat over medium. Cook until most of the fat renders, about 9 minutes. Raise the heat to medium high; add the sausage and cook, breaking it up with a wooden spoon, until lightly golden brown, about 9 minutes. Transfer the meat to the slow cooker (keeping the fat in the pan).
While the bacon and sausage are cooking, combine the flour, ground coriander, nutmeg, and pepper in a medium bowl. Dry the duck legs with a paper towel and dredge them in the flour, shaking off and reserving any excess flour. Place the thyme, peppercorns, bay leaves, coriander seeds, and cloves on a medium piece of cheesecloth, gather into a bundle, and secure with kitchen twine.
Add the duck legs to the hot fat in the pan and cook until golden brown on both sides, turning once, about 8 minutes total. Transfer the duck to the slow cooker, and then pour the beans on top.
Immediately add the onions, carrots, and garlic to the hot fat in the pan and sauté until the onions are softened, about 6 minutes. Whisk in the reserved flour and the mustard and cook until the flour is no longer visible, about 1 minute. Remove the pan from the heat and add the wine, then return the pan to the heat and raise the heat to high. Cook, whisking, for about 3 minutes. Add the stock and syrup and simmer for 2 minutes. Pour the sauce into the slow cooker and nestle in the spice bag.
Cover the slow cooker and cook on low until the duck is cooked through but not overcooked, about 4-1⁄2 hours. (The duck meat will have fallen off the bones.) Let the cassoulet sit for a few minutes, then remove and discard the spice bag and duck bones.
About 15 minutes before the cassoulet is done cooking, heat the oven to 400°F. Place the baguette slices on a baking sheet and toast until golden brown, about 12 minutes. Meanwhile, in a small bowl, mix together the butter, parsley, lemon zest, and salt. When the baguette slices come out of the oven, slather each toast with the butter. Serve a few in each bowl of cassoulet.