1. Have ready an ice bath in a large bowl. Place 2/3 cup sugar in a large saucepan, and set over medium heat. Cook until dark amber in color, about 6 minutes. Slowly add the milk and cream, whisking to dissolve the hardened caramelized sugar. Increase heat to high, and bring mixture to a boil.

2. In a medium bowl, whisk together the egg yolks, remaining 1/3 cup sugar, and salt until pale in color. Whisking constantly, add the hot cream mixture to the yolks. Return new mixture to saucepan, and set over medium heat. Cook, stirring constantly with a wooden spoon, until the cream coats the back of the spoon, 4 to 6 minutes.

3. Immediately remove pan from heat, and pour mixture through a fine sieve set over a heatproof bowl. Place bowl in ice bath, and stir occasionally until chilled.

4. Freeze in an ice-cream maker according to manufacturers instructions. Fold in the hazelnut brittle, and freeze overnight.

5. When ready to serve, scoop ice cream into individual caramel bowls.