Peel and cube potatoes. Cover with water and boil until tender, do not drain. Add the sugar,vanilla,cinn,butter. Mix cornstarch with 1/4 cup of water and add to potato mix.Cook on low while making bisquick dough roll dough out. In a 3 qt casserole add layers potatoes part of dough, layer potatoes and so on. Finish up with dough on top, sprinkle with sugar and dot with extra butter. Bake at 350*for 30 minutes or until dough is done..