Preheat oven to 350°F. Sift together dry ingredients. Add cranberries, milk, butter and vanilla. Mix well. Pour into a buttered 8-inch square baking dish. Bake at 350°F for 40 minutes.
While the cake is in the oven go ahead and make up the butter sauce. Combine the butter, sugar and cream in a saucepan. Bring to a boil and then lower heat. Stir in vanilla and cinnamon and simmer for 10 minutes. Serve the duff warm with the sauce on the side.