Melt the chocolate with two tablespoons of milk in the microwave or using a double boiler.
Add the melted butter and egg yolks, stirring quickly and vigorously.
Then add the icing sugar, ground hazelnuts, crème fraîche and a generous dash of hazelnut oil. Place in the fridge for 2 hours.
Form small balls with the palm of your hands and insert a whole hazelnut in the center of each.
Coat each truffle with crushed hazelnuts.
Store in the fridge until serving.