Add sugar to the heavy cream and whip. Chill in the fridge.
Break the chocolate bar into a heatproof dish, then melt in a microwave. Start with 10 seconds at 600 W, then continue heating with 10 seconds increments until it's half melted. The rest will melt with the residual heat.
Add the melted chocolate (after letting it cool a bit) into the chilled whipped cream. Mix it up.
The chocolate should become hard and fine. Add some more to taste.
Story Behind this Recipe
I was trying to make chocolate cream and made this by accident. In fact, I like this better than chocolate cream.
Since I came up with this by accident, I'm not sure if the recipe is foolproof, but the key is to whip the cream and chill it in the fridge.