Let the coffee brew to allow it to cool. Pour it into a deep plate.
Pour the very cold cream, the very cold mascarpone, the sugar and the vanilla into the bowl of the food processor or a large container. Beat at medium speed to obtain a firm whipped cream. It will gradually take shape. It must remain light but hold well.
Take a rectangular dish (mine is 20x28cm in internal dimensions).
Dip each sponge finger in the cold coffee: no more than 1 to 2 seconds so as not to soak it too much. Then place each biscuit in the bottom of the dish, pressing them together well to leave little space.
Spread a layer of whipped cream on the biscuits using a spatula.
Repeat the biscuit step to cover the whipped cream (dip them in the coffee and place them in the dish).
Spread a small portion of whipped cream to thinly cover the second layer of biscuits then pipe the rest of the whipped cream with a piping bag cut at the end (if you want the same decoration as me) OR simply place the second layer of whipped cream on top of the biscuits, smoothing with a spatula.
Add cling film and refrigerate overnight (minimum 5 hours, but I recommend overnight to be able to cut into portions, otherwise you can serve it with a large spoon).
Sprinkle with bitter cocoa through a small sieve before serving. Use a large knife to cut into clean pieces.
Notes
Egg-free tiramisu keeps in the refrigerator for up to 3 days. I advise you to cover your dish with cling film to protect it from fridge odors.