Place the kadaif in a large bowl and chop it roughly with kitchen scissors or a knife. In a large nonstick skillet, melt the butter over medium heat. Add the chopped kadaif and a pinch of salt. Stir constantly with a silicone spatula or wooden spoon for 5 to 7 minutes, until golden and crisp. Transfer to a medium mixing bowl and let cool.
In a small heatproof bowl, melt the white chocolate in the microwave in 20-second intervals, or over a double boiler, stirring until smooth. Mix in the pistachio paste until fully combined. Pour the chocolate mixture over the cooled kadaif and stir until evenly coated.
Line the bottom of a 10-inch/26 to 28 cm springform pan with parchment paper. Press the kadaif mixture firmly into the bottom of the pan using a flat-bottomed glass or measuring cup. Freeze while you prepare the filling.
Preheat the oven to 285°F (140°C).
In a stand mixer fitted with the paddle attachment, or in a large mixing bowl using a hand mixer, beat the cream cheese, heavy cream, sour cream, sugar, vanilla, cornstarch, and salt until completely smooth. Add the eggs one at a time, mixing just until incorporated. Do not overmix.
Pour the batter over the chilled crust and smooth the top. Place the springform pan on a baking sheet and bake on the center rack for about 1 hour, or until the edges are set and the center is slightly jiggly. Remove from the oven and cool at room temperature for 1 hour, then refrigerate for at least 4 hours or overnight.
For the ganache, place the white chocolate and cream in a small heatproof bowl. Heat in the microwave in 30-second intervals, or over a double boiler, stirring until smooth. Let cool for 5 minutes, then pour over the chilled cheesecake. Refrigerate for another hour, or until the ganache is set.
In a chilled mixing bowl, whip the heavy cream, powdered sugar, and vanilla extract using a hand mixer or stand mixer fitted with the whisk attachment. Beat on medium-high speed until soft to medium peaks form, about 2 to 3 minutes. Do not overwhip. Transfer the whipped cream to a piping bag fitted with a star or round tip. Pipe decorative swirls or rosettes over the ganache-covered cheesecake. Refrigerate for 30 minutes to set.
Serve chilled, topped with fresh raspberries.