Begin by preheating your oven to 375°F (190°C). Prepare an 8-inch round cake pan by greasing it lightly with butter and lining the bottom with parchment paper for easy removal. In a heatproof bowl, combine the chopped chocolate and cubed butter. Set this bowl over a pot of gently simmering water, creating a double boiler. Stir occasionally until everything is melted and smooth. Remove from heat and let it cool slightly.

In another bowl, whisk together the sugar and eggs until well combined. The mixture should become pale and fluffy. Gradually add the melted chocolate and butter mixture. Stir in the vanilla extract, instant espresso powder, cocoa powder, fine salt, and optional cinnamon. Mix until everything is well incorporated.

If you opted for it, and if you have it on hand, add the baking powder now. It helps create a slightly airy texture. Pour the batter into your prepared cake pan. Spread it out evenly and give the pan a bit of a tap on the counter to remove any air bubbles.

Place the pan in the preheated oven and bake for 20-25 minutes. Keep an eye on it; the top should look slightly set while the center remains soft. Once done, take it out and let it cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.

While the cake cools, let's whip up that delicious mocha cream. In a mixing bowl, combine the heavy cream, espresso powder diluted in warm water, cocoa powder, powdered sugar, and vanilla extract. Using a hand mixer or stand mixer, whip until soft peaks form. Don’t whip too long; you want a smooth, spreadable consistency.

Slice the cooled cake into rich wedges. Serve with a generous dollop of mocha whipped cream on top and perhaps a sprinkle of fresh raspberries for color and additional flavor. The presentation is beautiful and the taste is divine.