In a bowl, whisk the egg yolks, sugar and salt together until smooth and pale yellow.
In a saucepan, heat the milk over medium heat until it reaches a gentle simmer.
Continuously stir while slowly pouring about half of the hot milk into the bowl of whisked egg yolks. Mix well.
Pour the mixture back into the saucepan, and continue to stir over low heat until the cream slightly thickens, enough to coat the spoon, about 10 to 15 minutes.Temperature Notes - You should see evaporation during the last half of cooking - if not, the heat may be too low. However, to help prevent curdling, keep the mixture below 175°F (80°C) .
Remove from heat, stir in the hazelnut flour and mix well.
Chill - Let cool completely. Then refrigerate until cold - 2 hours to overnight.
Freeze - Process in an ice cream machine. (Alternately, freeze, stirring every 2 hours until solid, around 4 to 8 hours.)
Serve with a handful of chopped hazelnuts sprinkled on top and/or around.
Hazelnut Flour Substitutions
Whole unsalted hazelnuts, toasted and peeled - Pulse 1 cup in food processor to a sandy texture.
For a smoother texture, use half the amount of either:
Hazelnut Paste - For the absolute smoothest texture (look for 100% hazelnuts.)
Hazelnut Butter - Varies in coarseness, so get the finest texture you can find (look for 100% hazelnuts.)
Notes
Total Preparation Time does not include time to chill or freeze, due to variations in temperatures, quantities and freezing methods.
Storage - Store in tightly sealed container in freezer.
Serve it at its best - Let ice cream thaw 5 to 15 minutes at room temperature before scooping.