Sweet Potato-Cauliflower Shepherd's Pie
1 cup chicken broth 1 pound sweet potatoes, peeled and chopped 1 teaspoon salt 1 ½ pounds ground beef 2 carrots, diced 2 cloves garlic, minced 2 tablespoons light olive oil 2 tablespoons tapioca starch 3 tablespoons butter 3 tablespoons tomato paste ¼ cup chicken broth ½ cup corn ½ cup freshly grated Parmesan cheese ½ cup peas ½ onion, diced ½ pound cauliflower florets, chopped ½ teaspoon ground black pepper