Begin by placing the finely chopped dark chocolate into a heatproof mixing bowl, ensuring the pieces are uniform for even melting.
In a small saucepan, pour in the heavy cream. Heat over medium heat until the cream starts to gently simmer—watch carefully to prevent it from boiling over. Remove from the heat immediately once it simmers.
Carefully pour the hot cream over the chopped chocolate, allowing it to sit undisturbed for about 2 minutes. This waiting period will help the chocolate melt effectively.
After 2 minutes, add the hazelnut paste, vanilla extract, and a pinch of flaky sea salt to the bowl. Using a spatula, stir gently but thoroughly until the mixture is smooth and glossy, ensuring all ingredients are well combined.
Cover the bowl tightly with plastic wrap and place it in the refrigerator. Chill for approximately 1 hour, or until the chocolate mixture is firm enough to scoop.
Once the mixture is set, use a melon baller or a small spoon to scoop out portions. Quickly roll each portion into a smooth ball using your palms, ensuring a uniform shape.
Roll each chocolate ball in the finely chopped toasted hazelnuts or cocoa powder, coating them evenly for a delicious finish.
Arrange the finished truffles on a baking sheet lined with parchment paper to prevent sticking.
Once all truffles have been rolled and coated, refrigerate them again for about 30 minutes to help them set completely.
Notes
For an elegant display, arrange the truffles in a decorative box or a beautiful serving plate. Dust some of the truffles with cocoa powder and scatter a few whole hazelnuts around for a refined touch.