Preheat the oven to 350°F.

Spread on a rimmed baking sheet:

Toast until fragrant, stirring occasionally, 10 to 15 minutes. Immediately transfer the nuts to a clean kitchen towel. Wrap the nuts in the towel and rub vigorously to remove as much of the skins as possible. Let cool completely.

Reserve 6 hazelnuts for garnish. Finely grind the remaining nuts in a food processor, but not to a paste. Bring almost to a simmer in a medium saucepan:

Stir in the ground nuts. Remove the pan from the heat, cover, and steep for 30 minutes.

Strain the milk into a bowl, pressing on the nuts to extract as much liquid as possible; discard the nuts, and return the milk to the saucepan. Add:

Bring to a simmer, stirring occasionally to dissolve the sugar. Beat in a medium heatproof bowl:

Slowly whisk half the hot milk mixture into the eggs. Pour this mixture back into the saucepan and cook over low heat, stirring constantly, until the custard reaches 175°F and coats the back of a spoon. Do not allow the mixture to boil. Remove the pan from the heat and strain the custard through a fine-mesh sieve into a large bowl. Chill thoroughly. Whip to soft peaks:

Gently stir one-quarter of the whipped cream into the chilled custard, then fold in the remaining whipped cream. Spoon the mixture into 6 individual goblets. Place plastic wrap directly on the surface of the custards. Freeze until firm, for at least 3 hours. Garnish each goblet with a hazelnut. Serve immediately.