Preheat oven to 400° F.
Heat a large skillet over medium-high heat. Add the ground beef and chopped onion to the pan and cook, breaking up the meat, until the beef is browned. Drain off excess grease.
1 pound ground beef, 1 small yellow onion
Reduce the heat to medium. Add the garlic, frozen vegetables, flour and tomato paste. Cook stirring, for 1-2 minutes.
3 cloves garlic, 16 ounces frozen mixed vegetables, 2 tablespoons all-purpose flour, 2 tablespoons tomato paste
Add the beef broth, Worcestershire sauce, paprika, thyme, salt and pepper. Stir. Bring to a low simmer and cook for 10 minutes (reduce the heat as needed to keep it at a low simmer), until most of the liquid is gone. If the meat looks dry, you can add a little more broth. You want it to have some moisture, but do not want it soupy. Then remove pan from the heat.
1 cup low sodium beef broth, 1 tablespoon Worcestershire sauce, ½ teaspoon paprika, ½ teaspoon dried thyme, ½ teaspoon salt, ¼ teaspoon black pepper
Transfer the meat mixture to a 9x13-inch baking dish. Spoon the mashed potatoes over the top and then spread into an even layer. Use a fork to make some textured ridges on the mashed potatoes; these will crisp and brown in the oven.
Bake uncovered for 25-30 minutes until potatoes are golden brown on the edges. (Place a rimmed baking sheet on the rack below to catch any drips.) If desired, broil for 1-3 minutes to brown the potatoes in spots. Let stand for 5 minutes and then serve.