While the potatoes are cooking, heat olive oil over medium-high heat. Once hot, add diced onion, carrot and celery. Season with ½ teaspoon salt and cook until soft and translucent, about 5-7 minutes.
Add ground beef, black pepper, another ½ teaspoon salt, garlic cloves, tomato paste, Worcestershire sauce and mix, breaking up the ground beef.
Add in the thyme, rosemary, nutmeg and beef broth. Stir and cook the beef mixture for 6-8 minutes. Stir in 1 tablespoon of flour, cornstarch or arrowroot powder to thicken, cook for 2 more minutes.
Turn off the heat and add the mixture to a baking dish. I used a round dish but a 9x13 inch baking dish will work.
Spoon mashed sweet potatoes over the beef in a baking dish, careful not to mix the two. It helps if the filling is slightly cooled for this step. Using a fork make a zig-zag design. Top with a sprinkle of paprika.
Bake at 400 degrees F for 20 minutes. Broil for a few minutes on high if desired.