Put the chocolate in a large mixing bowl.
Stir together the cream, grappa, and a pinch of salt in a small saucepan over medium-high heat.
When the cream is steaming, but before it comes to a full boil, pour it over the chocolate and let stand for 2 minutes to melt the chocolate.
Vigorously whisk the chocolate and cream together until blended and completely smooth.
Transfer the bowl to the refrigerator to cool until firm, stirring occasionally, about 1 hour.
Pour a pile of cocoa onto a plate.
Drag a teaspoon across the surface of the solid chocolate repeatedly until you have a loosely piled spoonful.
If the chocolate is too hard to scrape, let stand at room temperature for a few minutes.
Lightly press the chocolate with your hands to make a walnut-sized nugget and roll it in the cocoa powder.
Avoid making the truffles perfect; they should be irregular and varied.
Repeat with the rest of the chocolate.
Transfer the finished truffles to a plate.
Store truffles in the refrigerator for about 1 week, but serve at room temperature.