Preheat oven to 350°F & grease 9x9-inch baking pan.

In a large mixing bowl, stir together the flour, sugar, cocoa, cinnamon, baking powder & baking soda.

Pour in the buttermilk, butter & vanilla & stir just to combine. Mix in the chocolate chips & turn the batter into the prepared pan.

In the same bowl, not washed, make the topping: mix the brown sugar, cocoa & cinnamon, then stir in the boiling water until smooth. Pour over the cake mix & put in the oven. Bake 35 minutes, just until the cake rises & is sitting in the midst of molten, bubbling chocolate sauce. Serve warm.