First, layer the duck legs in a casserole dish surrounded with kosher salt. Wrap this in plastic wrap and place it in the fridge for 4-6 hours.
Then, remove the duck legs from the salt, rinse them lightly, and pat them dry with a paper towel.
Afterward, submerge the duck legs in melted duck fat in a Dutch oven or ovenproof dish. Bring that dish up to a light simmer (not a boil), and simmer them lightly on the stove until the duck meat is extremely tender (up to 3 or 4 hours).
Remove the duck from the heat and allow to cool completely. Then, drain the fat from the duck legs and reserve the fat on the side.
Pull the duck meat and skin from the duck legs, making sure to discard all bones and chewy cartilage.
Place the duck meat and skin in a bowl and add the minced shallots, Dijon mustard, and parsley. Mix to incorporate and break up the duck into bite-size pieces.
Adjust the seasoning with salt and pepper and additional Dijon mustard if necessary.
Wash and pit the sour cherries.
Wash the oranges, then quarter them to remove any seeds.
Roughly chop the oranges, then grind them in food processor until the rind is in pea-size pieces or smaller.
Combine the sour cherries, ground orange, and sugar in a large pot and simmer uncovered, stirring frequently until the mixture is thick like a jam. Taste, and add more sugar or a little lemon juice if needed. If the orange rind still has an astringent bite, add a bit more water and continue to cook until that taste has disappeared.
Slice the baguette into 1/4"-thick crostini, and season the rounds with olive oil, salt, and pepper in a bowl.
Lay out the crostini in a single layer on a baking sheet lined with parchment paper.
Toast the crostini in a low-oven (250 degrees) for approximately 10 minutes or until they are nice and crunchy.
Then, spread a thin layer of sour cherry marmalade on each crostini followed by a dollop of duck confit.
Top each hors d'oeuvre with a small parsley leaf.