My Famous Homemade Shepherds Pie

To Assemble and Bake: 

1. Adjust oven rack to center position and preheat oven to 425°F (218°C).
2. Before assembling, heat cream in a large saucepan until simmering.
3. Add potatoes and stir gently until completely incorporated. Season with salt and pepper. Potatoes are now ready for assembly.
4. Set a 9- by 13-inch 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.)
5. Top with mashed potatoes, spreading them with a spatula to cover the surface completely.
6. Using spatula, create a dappled pattern on top of potatoes.
7. Sprinkle with grated Parmesan cheese, if using.
8. Transfer to oven and bake until top is browned and casserole is fully heated through about 20 minutes.
9. 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.)
10. Let stand 15 to 20 minutes before serving.
11. Casserole can be assembled, wrapped with plastic, and refrigerated up to 2 days.
12. Reheat in a 350°F oven for about 35 minutes, then use the broiler to brown top