For the cake, preheat oven to 325˚F. Fill a saucepan 1/3 of the way full with water. Place over medium heat and bring to a simmer. In a medium glass bowl, combine chocolate, butter, heavy cream and salt; set over simmering water, stirring occasionally, until chocolate and butter melt. Whisk to combine. Remove glass bowl from the heat and let cool slightly.

Combine eggs and sugar in a stand mixer fitted with a whisk attachment and whisk until very fluffy and pale yellow, about 3 minutes. Add vanilla and whip another minute more.

Once melted chocolate is cool to the touch, with the stand mixer running, pour into sugar mixture and mix until incorporated.

Grease a 9-inch springform pan with butter and dust with cocoa powder; pour off any excess. Place a round of parchment paper at the bottom.

Pour batter into pan and bake until the sides of the cake have risen and the top is glossy and dry, 40 to 45 minutes. Remove from oven to cool completely.

Once the cake has cooled, make the ganache. Over a saucepan partially filled with simmering water, melt chocolate, cream and liquor, then whisk until smooth. Remove cake from pan and peel off parchment paper. Place cake onto serving plate and pour ganache on top, leaving a ½-inch border. Sprinkle with nuts and salt. Let set for 15 minutes before serving.