Toast 1 cup kataifi with 2 tbsp butter until golden. Mix in 4 tbsp pistachio cream and 1/2 cup chocolate. Set aside.
Whisk eggs, almond milk, heavy cream, sugar, vanilla, cinnamon, and salt until smooth.
Layer half the challah, spread pistachio cream, add chocolate-pistachio filo mixture, top with remaining challah. Pour custard over, press gently, and let soak (15–30 min or overnight).
Bake at 350°F (175°C) for 40–50 minutes, until set and golden.
Toast another 1/2 cup kataifi in butter. Spread 1/3 cup pistachio cream over baked casserole, then sprinkle with toasted kataifi.
Serve warm