In a saucepot, melt butter, and stir in brown sugar, and coconut milk.
Heat oven to 350˚F. In a large pot on a very low flame, combine coconut milk and dark brown sugar. Once brown sugar has dissolved, stir in cassava, cooking and stirring about 5 minutes. Stir in vanilla, salt, and cinnamon. Into a 13-inch x 9-inch baking dish, pour enough of Topping to cover the base. Pour the Heavy Cake batter on top and bake 45 minutes to 1 hour, until batteris firm. Pour remaining topping over the cake, return t oven, and bake until topping is bubbly. Remove from oven and cool.