Crust

1. Preheat oven to 175°C (350°F). Grease and line the base and sides of a 9-inch (23 cm) springform pan with parchment paper. Set aside.
2. Place the butter in a small saucepan over medium heat. Cook, swirling occasionally, until the butter is golden, nutty, and flecked with brown solids, about 5 minutes. Remove from heat immediately and pour into a bowl to cool slightly.
3. Pulse the graham crackers and toasted hazelnuts in a food processor until finely ground. Add the sugar and salt and pulse to combine. Pour in the browned butter and pulse until the mixture clumps when pressed together.
4. Tip the crumb mixture into the prepared pan. Press it firmly and evenly across the base and up the sides to about ¾ inch. Bake for 10–12 minutes, until fragrant and lightly golden. Remove and cool completely on a wire rack. Lower the oven temperature to 120°C (250°F).

Filling

1. In the bowl of a stand mixer, beat the cream cheese until very smooth, 3–4 minutes. Scrape down the bowl. Add the sugar and beat on medium speed until incorporated and fluffy, 3 more minutes.
2. Add the eggs and egg yolk one at a time, beating well after each addition. Beat in the vanilla bean paste, dissolved coffee, coffee liqueur (if using), and salt. Add the crème fraîche and beat until the batter is very smooth, light, and well combined, about 4 more minutes.
3. Pour the filling over the cooled crust and smooth the top with an offset spatula.
4. Fill a deep roasting pan three-quarters full with water and place it on the lowest shelf of the oven. This creates a moist environment and prevents cracks.
5. Bake for 2½–2¾ hours, until firm around the edges and top with a slight jiggle remaining in the centre. Turn off the heat, pry the oven door slightly ajar, and let the cheesecake cool to room temperature in the oven, about 1 hour. Refrigerate, still in its pan, for at least 8 hours or overnight.
6. When completely cold, remove the springform rim and parchment. Carefully transfer to a serving plate. Top with the dark chocolate ganache.

Ganache

1. Place the finely chopped chocolate in a small bowl. Heat the cream in a saucepan until just about to boil. Pour the hot cream over the chocolate, let sit 1 minute, then stir with a rubber spatula until completely smooth. Cool for about 10 minutes until slightly thickened.
2. Pour the ganache over the chilled cheesecake, smoothing the top with an offset spatula. Refrigerate for 30 minutes to set. Sprinkle with flaked salt and serve.