Preheat the oven to 170°C and grease a 23cm springform cake tin with butter.
Zest three oranges into a large mixing bowl.
Process the deseeded orange flesh with rapeseed oil in a blender until smooth.
Whisk the eggs and 250g of caster sugar into the zest until pale and thick.
Stir the flour, ground almonds, and baking powder together in a separate bowl.
Fold half of the orange purée into the egg mixture.
Fold in the flour mixture followed by the remaining orange purée.
Pour mixture into the tin and bake for 60 minutes until a skewer comes out clean.
Whisk cream cheese, crème fraîche, and icing sugar together then chill until needed.
Julienne the zest of the remaining two oranges finely.
Simmer 150ml of water, 150g caster sugar, and julienned zest for 10 minutes.
Strain the zest through a sieve over a bowl.
Coat the strained zest in the remaining caster sugar on a plate.
Cool the cake slightly in the tin then transfer to a wire rack.
Frost the cooled cake and garnish with walnuts, candied zest, and basil cress.