First prepare the choux pastry: melt the butter in a thick-bottomed pan, together with the milk, water and salt, bringing to the boil.
Add the flour, already sifted, all at once, stirring vigorously with a wooden spoon until a light film begins to settle on the bottom, at which point remove from the heat and leave to cool.
Once almost completely cold, add the eggs one at a time, waiting until the first is completely incorporated before adding the second, then transfer the choux pastry into a piping bag with a smooth, not too thin nozzle.
Create the cream puffs on the baking tray lined with baking paper, spaced well apart.
Moisten a finger and use it to press the tip remaining on top of the cream puffs, so as to obtain puffy and round cream puffs.
Cook for about 10 minutes in a static oven preheated to 200°C, then lower to 180°C and cook for another 15-20 minutes, finally remove from the oven and leave to cool completely.
Dissolve the coffee in the water after heating it, then let it at least cool.
Combine the mascarpone, icing sugar and coffee in a bowl and mix, then add the very cold cream from the fridge and whip with the whisk until you obtain a smooth and well-whipped cream, then transfer it into a piping bag with a not too large nozzle. great.
Create a small hole in the bottom of the cream puffs and fill them with the cream.
Finally proceed with the decoration: melt the chopped chocolate (in the microwave or in a bain-marie), then, one at a time, dip the top part of the cream puffs and place a coffee bean on top.
The coffee puffs are ready: let the chocolate dry thoroughly before serving them.