Place the finely chopped dark chocolate into a heatproof mixing bowl.

In a small saucepan, gently heat the heavy whipping cream until it just reaches a simmer. Do not let it boil.

Pour the hot cream over the chopped dark chocolate. Let it sit undisturbed for 5 minutes.

Add the softened butter, vanilla extract, and salt. Whisk gently starting from the center until the ganache is smooth and completely combined.

Cover the bowl with plastic wrap touching the surface of the ganache. Chill in the refrigerator for at least 2 hours until firm.

Line a baking sheet with parchment paper. Scoop the chilled ganache into bite-sized mounds and roll them into smooth domes. Return to the fridge for 30 minutes.

Prepare the glaze: Melt the semi-sweet chocolate, butter, and corn syrup together in a double boiler over gently simmering water. Stir until perfectly smooth and glossy. Let cool slightly.

Place the chilled truffles on a wire rack set over a parchment-lined baking sheet. Spoon or pour the warm, glossy glaze over each truffle, allowing the excess to drip off.

Let set at room temperature for 10 minutes, then transfer to the refrigerator to harden the shell completely before serving.