Preheat oven to 325’. Butter an 8 inch round cake pan and line the bottom with a round of parchment paper or foil.
In a medium saucepan bring water and sugar to a simmer over moderate heat, stirring occasionally. Add butter and simmer stirring occasionally, until melted. Remove from heat and add chocolate, swirling pan to submerge chocolate in hot syrup. Let chocolate stand in syrup 3 minutes and whisk until smooth.
In large bowl whisk together eggs, coffee, rum, and cinnamon.
Add chocolate mixture, whisking until well combined, and pour into cake pan. Put cake pan in a larger baking pan and add just enough water to reach halfway up the side of cake pan. Bake cake in middle of oven 45 minutes, or until slightly form to the touch. Cool cake completely in cake pan on a rack.
Run a thin knife around edge of pan to loosen cake and put pan on warm stove burner 3 to 4 seconds. Invert cake onto a plate and remove parchment or foil.
Bring cake to room temperature.
In a bowl with an electric mixer or a whisk beat cream with sugar and cinnamon until it just holds stiff peaks.
Just before serving, spread cream over top of cake or spoon onto plates along-side individual pieces. I add a few raspberries to each plate!