Add the duck fat to a heavy pot and allow it to melt over low heat. Mix the salt, brown sugar, cinnamon, cumin and paprika in a small mixing bowl. Pat the duck legs with paper towels and sprinkle all sides generously with the spice mix. Refrigerate, uncovered, for 15 minutes.
Remove and place the legs skin-side up in the duck fat, making sure they're completely submerged. Add the peppercorns and coriander seeds. Using an instant-read thermometer, bring the duck fat to a lazy simmer, 165 to 175 degrees F. Gently confit the legs in the simmering fat until the duck is fork tender, about 2 1/2 hours. Remove and cool.
Meanwhile, add the reserved duck trimmings to a pan and cook to render the fat over low heat. Place onto a paper-towel-lined plate and reserve until serving.
Using a sharp knife, remove the skin from the legs. Using two forks, shred the confit following the grain of the protein. Mix with 1/4 cup of the confit fat.
Set a flat top griddle over high heat. Sear the skin on both sides to make a crunchy, cracklin'-style texture, about 7 minutes total. Finely julienne and set aside. Add the confit to the griddle in batches and crisp until golden brown, 2 to 3 minutes.
To assemble, spread Cranberry Jam onto the tops and bottoms of each bun. Build sliders with 2 ounces (about 1/4 cup) of confit, then a layer of crispy skin. Top with 2 tablespoons Fennel and Celery Root Slaw. Replace the top bun. Serve immediately with Butternut Squash Chips.
In a medium saucepot, bring the oil to medium heat. When the oil begins to shimmer, add the onions, season with some salt and pepper and brown for 5 to 7 minutes. Deglaze with the cranberry juice and stir to scrape up any browned bits. Add the cranberries and red wine vinegar. Simmer to completely soften the cranberries and until the jam is thickened and glossy, about 12 minutes. Remove from the heat and stir in lemon juice to taste. Season again with salt and pepper as desired.
Transfer to a serving dish and serve warm. Can be made ahead and refrigerated in an airtight container for up to a week.
Fennel and Celery Root Slaw:
In a large mixing bowl, briskly whisk the mayonnaise, sour cream, vinegar, dugar, mustard and salt and pepper to taste until smooth. Toss the celery root, carrots, apples, fennel and 2 tablespoons of the reserved fennel fronds into the dressing to coat evenly.
Cover with plastic and refrigerate for 30 minutes to allow the flavors to fully integrate.
Remove and toss again. Serve garnished with a few more fennel fronds.
Butternut Squash Chips:
In a small mixing bowl, thoroughly combine the salt, garlic powder, paprika, brown sugar, black pepper and cayenne. Set aside.
Using a sharp knife, cut the tubular top portion away from the globe-shaped bottoms of both squash. Using the knife or a mandoline, shave the tops into chips. Submerge the chips in a deep container with ice water for 10 minutes (this removes any extra starch and makes the chips crispy). Strain the chips and pat dry.
Meanwhile, using an instant-read thermometer, bring 3 inches of duck fat to 325 degrees F in a heavy gauge Dutch oven over medium heat. Working in batches, fry the chips until they are golden and crispy, 5 to 7 minutes. Transfer with a fine mesh strainer to a paper-towel-lined dish. Season immediately with a sprinkle of spice mix. Repeat until all chips are fried. Transfer to a large bowl and serve.