Preheat oven to 450 degrees.
Sift flour, baking powder, baking soda, salt, brown sugar and cinnamon and set aside.
Using a medium-size bowl, beat melted butter into the sweet potatoes. Add dry ingredients, stirring in a little at a time, alternating with buttermilk. Mix just well enough to moisten all ingredients. Form into a ball and turn out onto lightly floured board. Lightly pat top side with flour as well, since it is rather sticky batter.
Roll out to 1/2 to 3/4 -inch thickness with floured rolling pin. Cut with a floured biscuit cutter. Bake 20 to 25 minutes.