Preheat oven to 350ºF. Butter bottom and sides of a 9-inch springform pan. Line bottom with parchment paper, then butter the paper. Dust the inside of the pan with cocoa powder, tapping out excess.
Put chopped chocolate and butter in a large microwaveable bowl and microwave in 30-second increments, stirring between increments, just until it can be stirred smooth. Let cool.
Separate eggs, putting 4 of the whites in the bowl of a mixer and all 6 yolks into the warm chocolate mixture. Discard the remaining 2 whites. Whisk the yolks, coffee, cinnamon, and salt into the chocolate mixture until smooth.
Beat the 4 whites on medium speed until they form soft peaks when beaters are lifted, 3 to 4 minutes. Gradually add sugar and beat on high speed until the whites form stiff peaks when the beaters are lifted, 3 to 4 minutes more. Stir 1/4 of the whites into the chocolate mixture to lighten it. Gently fold in remaining whites.
Pour into the prepared pan and smooth the top. Put the pan into a larger pan, such as a roasting pan or a rimmed baking sheet, and put both pans in the bottom-third of the oven. Pour boiling water into the larger pan to come about 1-inch up side of cake pan.
Bake until torte is just firm to the touch and a toothpick inserted in the center comes out almost clean, 40 to 50 minutes.
Remove from water bath and let cool completely on a cooling rack. Spread on an even layer of whipped cream and top with raspberries if you like. Remove outside of springform pan to serve.
Tip: If you go for the whipped cream and raspberries on top (and why not?), garnish with a light dusting of cocoa powder.