Whisk the eggs, orange, salt, cut and scraped vanilla beans and caster sugar together in a stand-mixer for about 10-15 minutes to create a foam. Remove from the mixer and fold though the sifted flour until just combined.
Loosen the crème fraiche with a little of the cake batter before folding it though the remainder. Line a bundt cake tin by brushing it with melted butter and sprinkle with brown sugar.
Bake at 165°C for 25 minutes or until a skewer comes out clean. Remove from the oven and set for a few minutes at room temperature before un-moulding onto a cooling rack. Cool at room temperature.
For the frosting bring the crème fraiche, butter and zest to the boil in a saucepan, strain over the white chocolate and whisk together by hand until it is smooth and shiny. Leave to firm up for 15-20 or until it is a nice spreadable consistency.
Pre-heat the oven to 70°C. Boil the sugar and water together in a saucepan just until the sugar is dissolved. Leave it in the saucepan and add in the zest. Simmer on a low heat for 5 minutes. Strain the zest and coat in caster sugar. Separate the zest and place it on a lined tray. Place in the oven to dry out at 70°C for 30 minutes. Once cool place them on top of your cake.