Using a blender or pestle and mortar, blend or pound the hazelnuts until they are coarsely crushed.
Set the hazelnuts aside.
In a small saucepan, dissolve the gelatine in the water over low heat.
Set aside.
In a medium sized saucepan, bring the nuts and milk to the boil over moderately low heat, stirring constantly with a wooden spoon.
Remove the pan from the heat.
In a medium sized mixing bowl, beat the egg yolks and sugar together with a wire whisk or rotary beater until the mixture is pale and thick.
Pour the hot milk and nut mixture on to the egg yolk and sugar mixture, stirring constantly.
Return the mixture to the saucepan and replace the saucepan over low heat.
Cook, stirring constantly, for 2 to 3 minutes, or until the mixture thickens and is smooth.
Do not boil or the custard will curdle.
Remove the saucepan from the heat and stir in the dissolved gelatine and the coffee essence.
Pour the mixture into a medium sized mixing bowl and set it aside to cool.
In another mixing bowl, beat the cream with a wire whisk or rotary beater until it is thick but not stiff.
When the hazelnut mixture is quite cold but not yet set, lightly but thoroughly fold in the beaten cream with a metal spoon.
Pour the mixture into a 2 pint [1 1/2 quart] souffle dish or bowl, or into individual dishes.
Cover the dish and place it in the refrigerator leave for at least 4 hours, or until the cream is completely set and firm.
Remove the dish from the refrigerator and serve at once.