Season the chicken leg quarters generously with kosher salt. Refrigerate uncovered for 24 hours to dry-brine.
Preheat the oven to 425°F. Season the dry-brined chicken with the coarsely ground black peppercorns, all-purpose seasoning, rosemary, garlic, and chicken bouillon powder.
Place the chicken skin-side down in a hot skillet. Sear until the skin is crispy and golden brown.
Transfer the chicken to a baking dish and bake for 10 minutes while you prepare the sauce.
Melt the butter in the skillet. Add the diced shallot or onion and cook until softened.
Deglaze the skillet with the sherry wine or cognac, scraping up the browned bits. Add the chicken stock, heavy cream, and Dijon mustard. Simmer until the sauce lightly thickens.
Pour three-quarters of the sauce over the chicken. Return it to the oven and baste every 15 minutes until the thickest part reaches at least 165°F, avoiding the bone.
Rest briefly, then plate with the reserved sauce. Garnish with chopped parsley and serve.
Notes
The 24-hour dry brine produces better seasoning and crispier skin. Coarsely grind the peppercorns for the proper texture. Reserve one-quarter of the sauce for plating or later basting. Poultry should reach a safe minimum internal temperature of 165°F.