Toast the hazelnuts in a large frying pan over medium-high heat for 5 minutes., shaking the pan regularly so the nuts brown evenly. Remove from the heat and allow to cool completely.
Preheat the oven to 350°F
To make the crocanti, put one fifth of the cooled toasted hazelnuts in a food processor and process for about 1 minute, until they are finely ground. Place the ground hazelnuts, ½ cup of the sugar, the butter and cream in a saucepan over medium heat, stirring constantly, until the butter has melted and all the ingredients have combined.
Line a large baking sheet with a silicone sheet or some nonstick parchment paper and spread the hazelnut mixture on it thinly. Bake for 10-12 minutes in the oven,until lightly golden, watching carefully so it doesn't burn-the crocanti will melt further and spread on the tray. Remove and allow to cool and harden.
To make the soup put the remaining whole toasted hazelnuts, the remaining sugar and the water in a food processor and process for about 1 minute, until the hazelnuts are very finely ground. Strain through a fine sieve, pushing through as much of the liquid as possible and discarding the leftover nuts. Place the strained soup in a jar, cover and refrigerate for at least 4 hours, or preferably overnight.
To serve, place a ball of ice cream in a bowl and pour the hazelnut soup over it. Break the crocanti up into large pieces and scatter over the soup.
Servings 0