Heat the oven to 400 F. Place the potatoes in a medium pot with water and bring to a boil. The potatoes will take about 20 minutes to soften.
While the potatoes are cooking, heat oil in a medium saute pan over medium heat. Saute the onions and carrots until tender. Add the beef and turkey. Break apart the meat and stir frequently. When the meat is thoroughly cooked, add the tomato paste, rosemary, thyme, salt and pepper. Add the stock and cook for 10 minutes; stir in the peas and corn. Cook the mixture down until most of the stock is absorbed; place the mixture in a casserole dish.
When potatoes are soft, drain off the water. Then return potatoes to the pot over medium heat. Add the milk, butter and salt. Using an electric mixer or potato masher, mash the potatoes to a smooth consistency. Spread the mashed potatoes evenly over the top of the meat mixture and bake for 20 minutes or until slightly golden brown around the edges. Serve hot.
