Hot Chocolate Baked French Toast

Butter a 13x9" baking dish. Arrange bread slices in overlapping rows in dish. Cook cream, milk chocolate, semisweet chocolate, and vanilla in a medium saucepan over medium heat, whisking constantly, until chocolate is melted, about 5 minutes; remove from heat. Transfer 1 cup chocolate mixture to an airtight container; let cool to room temperature, then cover and chill until ready to serve. Reserve remaining chocolate mixture. Whisk eggs, milk, sugar, and salt in a large bowl. Whisking constantly, pour in hot chocolate mixture in a slow, steady stream. Pour evenly over and between each layer of bread. Push down with your hands to soak top of bread. Cover dish tightly with foil and chill at least 2 hours. Preheat oven to 350 °F. Bake foil-covered bread until warmed through and a knife inserted into the center feels warm to the touch, about 35 minutes. Remove foil and continue baking until bread is browned, 35 –40 minutes longer. Let cool 10 minutes. Meanwhile, toast hazelnuts in a small skillet over medium heat, tossing occasionally, until golden-brown and fragrant, 3 –5 minutes. Microwave 1 cup reserved chocolate mixture in a microwave-safe bowl in 10-second intervals (or heat in a heatproof bowl set over a saucepan of simmering water), stirring occasionally, until warmed through. Serve French toast with hot chocolate sauce and toasted hazelnuts.