Preheat the oven to 350 degrees F (175 degrees C). Lightly grease a 9 inch springform pan.
Combine the chocolate and ground espresso in a metal bowl, and set the bowl over a pan of simmering water. Stir occasionally until melted and smooth. Remove from heat and set aside.
In a large bowl, cream together the butter and sugar until light and fluffy. Beat in the egg yolks one at a time, mixing well after each one. Sift together the flour, baking soda, salt and cinnamon; stir into the butter mixture. Stir in the chocolate and espresso mixture. In a large clean glass or metal bowl, whip the egg whites until stiff peaks form. Fold in about 1/3 of the egg whites, blending well to lighten the mixture, then fold in the remaining egg whites gently. Spread the batter evenly in the prepared pan.
Bake for 60 to 70 minutes in the preheated oven, or until the top appears dry and cracked. A toothpick inserted into the center should come out clean. Cool cake in the pan over a wire rack. Dust with confectioners' sugar before serving, if desired.
