1 (32-ounce) bag frozen shredded hash brown potatoes, thawed
1 tablespoon canola or vegetable oil
1 pound ground beef
1/2 teaspoon kosher salt
1/4 teaspoon freshly ground black pepper
1/2 medium onion, diced
1 tablespoon all-purpose flour
3/4 cup low-sodium beef broth or stock
3 tablespoons Worcestershire sauce
1 (10-ounce) package frozen peas and carrots, thawed
Arrange a rack in the middle of the oven and heat to 425°F. Coat the wells of a standard 12-well muffin tin with cooking spray; set aside.
Press about 1/3 cup of shredded potatoes into the bottom and up the sides of each muffin well. Be sure the potatoes are packed tightly, cover the bottom well, and press up the sides of each muffin cup in an even layer.
Bake until the potatoes pull away from the sides of the muffin wells and the edges are golden-brown, 20 to 25 minutes. Set aside, and lower the oven temperature to 350°F. Meanwhile, prepare the filling.
Heat the oil in a large skillet over medium-high heat until shimmering. Add the ground beef, salt, and pepper. Break the meat apart with a wooden spoon and stir occasionally until all the meat is crumbled, browned, and cooked through.
Add the onion and cook, stirring occasionally, until soft and translucent, 4 to 5 minutes. Add the flour, stir well to combine with the meat and onions, and cook for 1 minute. Pour in the stock and Worcestershire sauce, scraping up any browned bits from the bottom of the pan. Once the sauce is bubbling, stir in the carrots and peas. Cook just until heated through, about 2 minutes. Remove the pan from the heat.
Divide the meat and vegetable mixture among the potato cups. Cover the muffin pan with aluminum foil and bake for 10 minutes. Cool for 2 to 3 minutes before removing the shepherd's pie cups and serving.