Steam the Japanese sweet potatoes over boiling water in a covered pot until tender, about 15 to 20 minutes. Remove and drain; set aside.
To make the meat filling, heat the olive oil in a large skillet over medium-high heat. When the oil is shimmering, add the onion, garlic, carrots, and celery and saute for about 10 minutes, stirring occasionally.
Add the ground beef, Mural of Flavor herb mix, and 1/2 teaspoon of sea salt. Saute, gently breaking up the meat and turning, until it is browned. Add 1 cup of beef broth and the tomato paste. Stir until well combined and transfer the mixture into a 9-by-13 inch casserole dish.
Heat oven to 350 F.
To prepare the potato topping, add the Fox Point herb blend and 1/2 cup of beef broth. Using a hand mixer, mash until smooth, adding more broth as needed. The potatoes should not be too dry. Add sea salt and pepper to taste.
Spoon the potato mixture over the meat mixture and bake uncovered for 45 to 60 minutes. The potatoes should be nicely browned.