Brown ground beef longer than usual and then strain off the fat and set aside. Put diced onion and shredded carrots in skillet and cook on low until soft. Add celery and season mixture with salt and pepper. Add ground beef and heat through.Add rosemary, thyme, garlic, butter, and flour and mix well. Add peas and beef stock and bring to a simmer. Pour into oven-safe 8X8 or pie pan and top with mashed potatoes, pricking potato layer with a fork. Sprinkle with parmesan. Bake in 375-400 degree oven for 30 minutes until the top is crisp. Enjoy!