Set a small glass mixing bowl over a small saucepan of simmering water and place the chocolate in the mixing bowl. Stir until the chocolate is completely melted and smooth.
Taking one muffin liner at a time, place 1 teaspoon of melted chocolate into each cup and tilt slightly so the chocolate coats partway up the sides. Place muffin liner back into tin and repeat with the remaining cups.
Using the palms of your hands, roll 1 teaspoon vanilla hazelnut butter into a slightly flattened ball and place in the center of each cup. Repeat with the remaining hazelnut butter until all cups are filled.
Pour enough melted chocolate over the hazelnut butter to cover completely and form a smooth top, about 1 heaping teaspoon.
Sprinkle coarse salt on top and chill in the refrigerator to set. Store in an airtight container at room temperature or in the refrigerator.