In medium sauté pan, heat olive oil over medium heat. Sauté celery, carrot, onion, parsnip, celery root and garlic until translucent, 8–10 minutes. Season with salt and pepper to taste. Set aside and allow to cool.
In large mixing bowl, whisk together eggs and heavy cream for 20 seconds. Stir in ground turkey, bread crumbs, chestnuts, and rosemary, sage and thyme leaves until incorporated. Stir in sautéed vegetables and season stuffing with salt and pepper. Set aside.
Line large cutting board with 24-inch square of plastic wrap. Evenly sprinkle salt and pepper over plastic wrap. Carefully lay turkey breast flat and skin side down on seasoned plastic wrap.
Generously season inside of turkey breast with salt and pepper. With rubber spatula, evenly spread reserved stuffing inside turkey breast, leaving 2-inch border on all sides.
Carefully roll turkey breast lengthwise, keeping stuffing inside and making sure not to catch plastic wrap inside roulade. Once you have a neat roll, cover with plastic wrap and securely tie ends with butcher’s twine. Refrigerate roulade at least 8 hours or overnight.
Day of roasting, remove roulade from refrigerator and preheat oven to 400 Cut eight 12-inch pieces of butcher’s twine and set aside. Carefully remove plastic wrap from roulade. Use butcher’s twine to tie roulade every 3 inches, starting in the center and working toward each end. Do not tie too tightly as stuffing may expand during roasting.
Before roasting, pat roulade dry with paper towels, brush skin all over with melted butter and season with salt and pepper. In roasting pan with rack, set roulade in center of rack and roast until internal temperature is 165 degrees F, about 1 1/2–2 hours.
Remove roulade from oven, transfer to cutting board and let rest for 20 minutes. Use kitchen shears to remove butcher’s twine. With sharp carving knife, slice roulade into 1/4- to 1/2-inch slices and arrange on serving platter. Sprinkle with sea salt just before serving.