Preheat oven to 400°F.
In a medium size sauce pot, whisk together the tapioca starch and half and half. Add the butter, garlic, rosemary (or thyme), salt and pepper. Heat just until the butter has melted. Remove from heat and whisk again.
Grease a 2qt baking dish.
Arrange the sweet potatoes in the dish by fanning them out in a pretty pattern of your choice.
Pour cream mix over the sweet potato slices. Working in between some of the slices to incorporate throughout the dish.
Bake uncovered for 30 minutes. Sprinkle with the parmesan cheese and bake for another 15 minutes or until golden brown. Serve warm.
