Gravy-Braised Turkey Legs with Cipolline Onions

Generously season turkey all over with salt and pepper. Let sit on a large rimmed baking sheet about 1 hour to bring to room temperature.

Heat oil and butter in a large Dutch oven or other heavy pot over medium. Place 1 cup flour on a plate and dredge turkey in flour, coating only the skin (do not shake off excess). Cook, outer side down, until very well browned (do not cook on inner side), 5–8 minutes. Transfer to a plate.

Add yellow onion, leek, celery, garlic, and peppercorns to pot, season with salt, and cook, stirring often and scraping up brown bits from bottom of pot, until vegetables are softened and beginning to brown around the edges, 10–12 minutes.

Sprinkle in remaining 2 Tbsp. flour; cook, stirring, 2 minutes. Add wine, bring to a boil, stirring, and cook until pan is almost dry. Add thyme, bay leaves, and 3 cups stock, season with salt, and bring to a simmer. Place turkey back in pot, browned side up, and add stock as needed to almost completely cover without submerging browned skin (this will keep it from getting soggy). Bring liquid to a very gentle simmer and cook until turkey is cooked through and an instant-read thermometer inserted near bone of thigh registers 165°, 35–45 minutes. Transfer turkey to plate.

Add cipolline onions and remaining stock to pot and simmer until tender, 20–25 minutes. Using a slotted spoon, transfer onions to plate with turkey. Simmer braising liquid until reduced to about 3 cups, 15–20 minutes.

Beat yolk and cream in a small bowl; stir in 1 Tbsp. braising liquid to warm. Whisking constantly, gradually add yolk mixture to braising liquid and remove from heat (if gravy boils after this point, it will curdle). Strain gravy into a large bowl. Wipe out pot. Return gravy to pot; taste and adjust seasoning with salt and pepper if needed. Return turkey, browned side up, and cipolline onions to pot and keep warm over low heat until ready to serve.

Serve topped with parsley.

Do Ahead: Legs can be seasoned 1 day ahead. Chill uncovered. Bring to room temperature before using.