In a small bowl, whip the heavy cream, sugar, and vanilla with an electric mixer until soft peaks form.
Add the mascarpone and whip just until the mixture holds stiff peaks and looks thick and smooth.
Pour the room-temperature coffee into a shallow bowl and stir in the brandy, if using.
Dip each ladyfinger into the coffee for 2 to 3 seconds, turning to coat both sides, and break them in half as needed to fit the ramekin.
Arrange a layer of dipped ladyfingers across the bottom of a 10-ounce ramekin.
Spread half of the mascarpone cream evenly over the ladyfingers.
Add a second layer of dipped ladyfingers, then spread the remaining cream on top and smooth it level.
Dust the top with cocoa powder using a small sieve.
Refrigerate for at least 2 hours, until the ladyfingers soften and the layers set, before serving.
Notes
Ladyfingers: If your store doesn't carry them, make your own with my small batch ladyfingers recipe. It makes 5 to 8, enough for this tiramisu with a few left over.Start with cold cream: Keep the heavy cream in the fridge until the moment you whip it. Cold cream whips faster and holds more air, which gives you a thicker filling that stands up in layers.Whip just to stiff peaks, then stop: Once you add the mascarpone, whip only until the mixture holds a firm peak and looks smooth. Overwhipping past that point turns the filling grainy and heavy.Bring the mascarpone to room temperature: Let it sit out for 20 to 30 minutes before you start. Cold mascarpone stays stiff and leaves lumps in the cream, while room-temperature mascarpone folds in smooth.Match the ladyfingers to your dish: A 10-ounce ramekin fits about 4 to 5 ladyfingers per layer once you break them to size. Snap them to fill each layer fully so every bite has cream and ladyfinger together.Give it the full chill: Refrigerate for at least 2 hours before serving, and longer is even better. The chill is what lets the ladyfingers soften into the cream and the layers set enough to hold their shape on the spoon.To make "Tiramisu For Two", double the ingredient amounts and use a 5x5 inch dish.