Gianduja Chocolate Cheesecake

Preheat oven to 300 degrees F (150 degrees C). Generously butter a 9-inch springform pan. (5 minutes)

Lay one sheet of phyllo dough in the prepared pan, gently tucking it into the base and allowing the edges to overhang. Brush lightly with melted butter. Repeat with the remaining phyllo sheets, layering them one at a time and brushing each with butter. Ensure the final layer is also brushed with butter. Cover the phyllo-lined pan with a damp cloth to prevent it from drying out. (15 minutes)

In a double boiler set over simmering water (or in a heatproof bowl set over a saucepan), combine the gianduja chocolate and unsweetened chocolate. Heat, stirring occasionally, until the chocolate is completely melted and smooth. Remove from heat and let cool to lukewarm. (20 minutes)

In a large bowl, beat the mascarpone cheese with an electric mixer until smooth and creamy. Gradually add the sugar, beating until well combined. Beat in the egg yolks one at a time, ensuring each is fully incorporated before adding the next. Stir in the cooled, melted chocolate mixture and hazelnut liqueur until evenly blended. (10 minutes)

In a separate clean, dry bowl, beat the egg whites with an electric mixer until stiff peaks form. Gently fold one-third of the beaten egg whites into the mascarpone mixture to lighten it, then carefully fold in the remaining egg whites until just combined. Be careful not to overmix, as this will deflate the whites. (10 minutes)

Pour the filling into the prepared phyllo-lined pan. Gently tuck the overhanging edges of the phyllo dough into the pan to create a rustic rim. (5 minutes)

Bake in the preheated oven for 45-60 minutes, or until the filling is set around the edges but still slightly loose in the center. Turn off the oven, prop open the oven door slightly with a wooden spoon, and let the cheesecake cool in the oven for 1 hour. This helps prevent cracking. (60 minutes)

Transfer the cheesecake to the refrigerator and chill completely for at least 4 hours, or preferably overnight, before serving. (240 minutes)