Shepherd's Pie is one of the most comforting of one pot meals going. My version calls for ground turkey instead of beef or lamb and to make it the perfect busy week night dinner I use frozen vegetables rather than fresh. Then I throw in some lovely leeks and diced onion, a bit of fresh thyme and a few spices, smother everything in gravy and top it with a lovely crust of mashed potatoes and holy cow deliciousness! —beetsandbluecheese.com
Preheat oven to 400°F. Heat oil over medium heat in a large sauté pan. Add the leeks and onions and cook until transparent, about 5 minutes. Add the turkey and cook, breaking up any large chunks, about 6-8 minutes or until just cooked through.
Stir in the flour, garlic, poultry seasoning, thyme, salt and pepper and cook 2 more minutes. Stir in the chicken broth and all the frozen veggies and stir to mix thoroughly. Bring to a simmer and cook until slightly thickened, about 5-7 minutes.
Grease a deep ceramic baking dish and add to it the turkey mixture. Top with the mashed potatoes and bake until browned on top and the mixture is bubbling, about 15 minutes. If the potatoes have not browned enough turn on the broiler for a few minutes to crisp them up. (Alternately to really make this a one pot meal you can sauté everything in a ovenproof skillet, top it with the mashed potatoes and slide the whole thing into the oven to bake.)
Let the casserole sit for 10 minutes before serving.