Preheat oven to 350 degrees Fahrenheit (180 degrees Celsius).

Place the hazelnuts on a baking sheet and bake for 10–13 minutes. Remove from oven and place on a dish towel. Rub vigorously in the towel to remove the skins.

Place the cooled hazelnuts in a food processor fitted with the blade attachment. Add oil and sugar and run until smooth, and fully combined, about four minutes.

Melt chocolate in a double boiler or in a bowl placed on top of a pot of boiling water. Once chocolate is fully melted, add the egg yolks slowly, mixing constantly while adding.

Add the dissolved cocoa and then the hazelnut butter, mixing until a smooth consistency is reached.

Meanwhile, beat the egg whites. When almost stiff, add confectioners’ sugar and continue beating until stiff peaks form.

Add some of the whites into the chocolate mixture and stir, and then fold the chocolate mixture into the whites until just combined. Place in individual glass cups or dessert bowls. Place in the fridge to set. 

Once mousse is firm, make the topping by melting chocolate in a double boiler.

Add the parve whipping cream and stir to combine. Pour over the mousse and freeze again. Before serving, you can garnish with nuts and white chocolate.