Set the glass/metal bowl over a pot of simmering water.
Add the heavy cream and vanilla until hot (watch carefully to avoid overheating and scalding cream).
Add the chocolate pieces and stir until melted.
Remove the bowl from the heat and stir in the butter.
Refrigerate for about 2 hours, until the mixture is very thick and hard to move.
Scoop to create one-inch balls, rounding them lightly with oiled hands.
Place balls on the parchment paper and sprinkle each with a several sea salt flakes (or to liking).
Store in a sealed container in the fridge.