Begin by preparing the crust, which serves as the foundation for your cheesecake. Mix together 1½ cups muesli, 6 tbsp melted butter, and 3 tbsp dark brown sugar until well combined, then press the mixture evenly over the bottom of an 8-inch loose-bottomed or springform cake pan.
Place the crust in the refrigerator to chill while you prepare the filling. Next, melt 4 oz of dark chocolate broken into pieces in a small heatproof bowl set over a pan of hot water, stirring occasionally until smooth, then allow it to cool slightly.
In a separate heatproof bowl, sprinkle 2 tbsp powdered gelatin over 3 tablespoons of cold water and let it sit for 10 minutes until it becomes spongy. Stand this bowl in a pan of hot water and heat gently until the gelatin dissolves completely.
While the gelatin dissolves, beat 8 oz of full-fat cream cheese until smooth and creamy. Add 2 large egg yolks and ¼ cup granulated sugar to the cream cheese, beating until the mixture is well blended.
Stir in ⅔ cup sour cream, the cooled melted chocolate, 1 oz of coarsely chopped dark chocolate chips, and the dissolved gelatin, mixing thoroughly to guarantee all components are evenly incorporated. In a separate bowl, whisk 2 large egg whites until they form stiff peaks but are not dry.
Carefully fold the whisked egg whites into the chocolate mixture using a spatula or large metal spoon, folding gently until evenly mixed to maintain the airiness of the whites.
Pour the chocolate filling onto the chilled muesli crust and refrigerate until the cheesecake is completely set. Once set, use a knife to loosen the sides of the cheesecake from the pan, then carefully remove the cheesecake and slide it onto a serving plate.
Complete the dessert by piping rosettes of 1¼ cups whipped cream on top and decorating with chocolate curls for an elegant finish.
