To toast hazelnuts, preheat oven to 350 degrees F and arrange hazelnut in single layer on baking sheet. Bake for 5 minutes, stir, then another 5 minutes. Remove from oven and let rest until cool enough to be handled. Place hazelnuts in a kitchen towel and rub to remove the skins. Place in food processor and pulse until finely chopped.
In a medium saucepan, whisk together milk, 1 cup cream, sugar, and salt over medium heat. Once heated, but not boiling, add hazelnuts. Cover and let rest for 1 1/2 hours.
In a large bowl, add chopped chocolate. In a small saucepan, heat remaining 1 cup cream just to boiling. Pour over chopped chocolate and whisk until chocolate is melted and blends with cream.
Strain the hazelnut milk back into medium saucepan, squeezing the solids to get as much liquid as possible. Discard the solids. Place the saucepan back over medium heat.
In a medium bowl, beat together egg yolks. While constantly whisking, pour about 1/4 cup (1 tablespoon at a time) into egg yolks. Continue to whisk and pour warmed eggs into saucepan. Constantly stir the mixture with a wooden spoon until thickened. It should be thick enough to coat the spoon. Strain the mixture into the chocolate cream, mix in vanilla, and stir until combined. Refrigerate until chilled.
Pour chilled mixture into ice cream maker and follow manufacturer's directions to create gelato. Serve immediately or pour into freezer safe container and freeze until desired consistency.