Twist on the classic, we liked using "Beyond Beef" to substitute ground beef.
For the Mashed Potatoes:
2 large russet potatoes, 1 yellow potato peeled and cut into 1-inch pieces
3 tablespoons unsalted butter, cubed
For the Meat Sauce:
2 cups chicken stock
1 packet unflavored gelatin
2 tablespoons vegetable oil
1 pound "Beyond Beef", ground beef or lamb, or some combination, or
1/2 yellow onion, diced
2 medium carrots, diced
1 rib of celery, diced
1 tablespoon garlic powder
1 tablespoons tomato paste
1 tablespoon dried thyme/ 1 sprig of thyme
1 bay leaf
1 teaspoon Marmite
Kosher salt and freshly ground black pepper and white pepper for mashed potatoes
3 tablespoons sourcream
1/2 cup of milk
1. For the Mashed Potatoes: Rinse potatoes to remove starch, boil potatoes until a knife easily pierces them. Drain potatoes in colander, then rinse with hot running water for 30 seconds.
2. Using a potato masher, food mill, or ricer, mash potatoes with butter into pot. Set aside.
3. Adjust oven rack to center position and preheat oven to 425°F (218°C).
4. Meanwhile, for the Meat Sauce: Place stock in a 2-cup liquid measuring cup, sprinkle with gelatin, and set aside.
5. Heat oil in a large Dutch oven over high heat until shimmering. Add ground meat and cook, stirring and scraping bottom of pot, until well browned; use a potato masher or large whisk to break up meat; lower heat as necessary to prevent scorching. Ladle out excess fat. Add onion, carrots, celery, and garlic and cook, stirring and scraping bottom of pot, until just beginning to soften.
6. Add tomato paste, half of the broth and cook, scraping up any browned bits. Add the rest of the chicken stock, thyme, bay leaf, and Marmite. Simmer until sauce is reduced and thick. Discard thyme sprigs and bay leaf. Season with salt and pepper.
7. To Assemble and Bake: Stir in cream and milk into mashed potatoes and heat until simmering. Season with salt and white pepper. Potatoes are now ready for assembly.
8. Set an 8 x 8 baking dish on a foil-lined rimmed baking sheet. Add meat sauce, being careful not to fill more than halfway. (You might not need all of the sauce, depending on the exact size of your baking dish.) Top with mashed potatoes, spreading them with a spatula to cover surface completely. Using spatula, create a dappled pattern on top of potatoes.
9. Bake until top is browned and casserole is fully heated through, about 20 minutes. For deeper browning, place casserole on a rack set about 6 inches under a hot broiler for the last few moments of cooking. (Monitor closely to prevent potatoes from burning.) Let stand 15 to 20 minutes before serving.
Casserole can be assembled, wrapped with plastic, and refrigerated up to 2 days. Reheat in a 350°F oven for about 35 minutes, then use broiler to brown top.