Shepherd's Pie with a Potato-Buttermilk Ranch Crust

Preheat oven to 375°F.

In a large bowl, combine the mashed potatoes with the dressing until smooth.

Heat oil in a large skillet over medium-high heat and cook the onions until they have softened and turn golden, about 5 minutes. Add the ground meat, generously season with salt and pepper, and cook, breaking up any clumps of meat with a wooden spatula, until the meat is browned, another 5 minutes.

If needed, drain any excess fat from the meat mixture, then stir in the frozen peas and carrots. Pour the mixture into a 1½-quart baking dish and spread mashed potatoes evenly over the top; bake uncovered for 30 minutes, or until golden.