Preheat the oven at 180 degrees Celsius.
Melt the butter in a casserole.
Crush the biscuits in an electrical blender. Mix it together with the melted butter.
Pour the mixture in a round baking form with removable edges. Press out the pie bottom so it covers the bottom and half the sides of the baking form.
Place the pie bottom in the middle of the oven for 10 minutes.
Time to prepare the filling while the bottom is in the oven. Start by pouring the egg yellows and the condensed milk in a bowl and whip for 3 minutes. Add the lime juice and continue whipping for 1 more minute.
Take out the pie bottom from the oven and pour the filling gently on the pie bottom. Place in the middle of the oven for 15 minutes.
Take out the pie and let it cool down.
Whip the cream to a hard foam, and then mix it with the creme fraiche.
Add the vanilla sugar and mix it all well. Place in the fridge for 30 minutes.
Cover the pie with the topping and place it in the fridge until it is time to serve it.