Heat oven to 350 degrees Fahrenheit. Grease a 9-inch round springform pan with butter and line with parchment paper.
Make the cake: Place butter, chocolate and hot coffee in a large heatproof bowl and mix well until melted and smooth. Whisk in sugar until dissolved. Add eggs and vanilla extract and whisk until combined. Sift flour, cocoa powder and salt together and whisk into the chocolate mixture.
Pour batter into the prepared pan and bake for 1 hour, or until a skewer inserted into the center comes out clean. Leave to cool for 20 minutes before removing from the pan.
Make the chocolate ganache, if desired: Process chocolate pieces in a food processor until fine. Heat cream and corn syrup until bubbles appear, then pour into the food processor with the chocolate. Process until smooth.
Scrape the ganache into a bowl and cover with plastic wrap. Set aside until it reaches the desired consistency.
Make the espresso cinnamon mascarpone cream, if desired: Beat all ingredients in an electric mixer until soft peaks form.
Peel the parchment from the cake and transfer to a serving platter. Spread ganache on top of the cake and slice into wedges. Serve with mascarpone cream, if using.