Mix the applesauce, mustard, walnuts, 1 sprig of finely chopped rosemary (leaves only), and garlic in a bowl. Set aside.
Season pork rack with salt and pepper. In a casserole dish, heat 15 mL (1 tbsp.) of butter over medium-high heat. Sear pork for 2 minutes on each side. Remove rack of pork from casserole and set aside.
Reduce heat to medium. In the casserole dish, heat the rest of the butter and brown the apples for 2 minutes. Deglaze with the white wine and reduce by half. Add the maple syrup, bring to a boil, and then add the chicken broth. Remove from heat.
Coat pork with reserved applesauce mixture and place it on top of the browned apples in the casserole dish. Add the remaining rosemary sprigs and bake until internal temperature reaches 65°C (150°F), about one hour. Remove from the oven and cover with foil. Let sit 15 minutes before serving.
Serve meat pink with pan drippings, baked apples, and baby potatoes.