1. Preheat oven to 400°.
2. Toss apples with butter and lemon juice in a lightly greased 13- x 9-inch baking dish or shallow ovenproof Dutch oven. Bake at 400° for 20 to 25 minutes. Season tenderloin with salt and pepper; brown in hot oil over medium-high heat in a heavy-bottom skillet 7 minutes. Remove apples from oven; place tenderloin in center of baking dish. Set aside.
3. Cook onion in skillet 5 minutes. Turn heat to high, and add wine; cook about 2 minutes, scraping bottom of skillet. Stir in cream, mustard, and rosemary.
4. Pour cream mixture over tenderloin, and bake at 350°, basting occasionally, 20 to 25 minutes or until meat thermometer inserted into thickest portion registers 155°. Let stand 5 to 10 minutes. (The pork will continue to cook.) Slice into 1/2- to 3/4-inch slices, and serve with apples and mustard cream sauce.