Bring 2 cups heavy cream (500 grams) to a boil. Meanwhile, soak 2 tablespoons powdered gelatin (25 grams) in cold water. When the cream boils, add the gelatin and stir until dissolved. Mix in the remaining heavy cream, pour into a mold, and freeze overnight.

Remove the panna cotta from the freezer and let it thaw for half a day.

For the brittle: Melt the sugar in a small saucepan, then stir in the hazelnuts.