Place the whole, washed and unpeeled oranges in a pan and cover with cold water. Bring up to the boil and simmer gently for about 2 hours – until they are completely soft. You may need to occasionally top up the water level.
Drain, cool and remove the stalks, cut in half and remove any seeds. In a food processor, blitz to a purée adding the elderflower cordial. A much quicker method is to prick the oranges all over with the point or a skewer and microwave for 8-10 minutes until completely soft.
Preheat the oven to 190ºC/Fan170ºC/Gas 5. Lightly butter 2 x 20cm round tins and line the bases with baking parchment. Melt the butter in a small pan (or in the microwave) and set aside to cool. Sift the flour, baking powder and salt into a bowl, tip in the ground almonds and set aside.
In an electric mixer using the whisk attachment, or a large bowl and electric whisk, beat the eggs and sugar until they become pale, fluffy and thickened (about 5 minutes). Using a large spoon or spatula, gently fold in the cooled melted butter, the flour mixture and the orange pulp. Divide between the 2 prepared tins and bake for about 25-30 minutes, or until a skewer comes out clean or it springs back to the touch.
Meanwhile make the syrup by mixing the cordial and sugar together in a little bowl. As soon as the cakes come out of the oven prick all over with a cocktail stick and pour syrup evenly over the cakes. Leave to cool in their tins.
When ready to assemble, simply split each cake in half horizontally. Soften the mascarpone in a bowl by mixing it and then stir in the crème fraiche. Gradually add the vanilla, elderflower cordial and caster sugar mixing all the time.
Cut the passion fruit in half and scoop out the pulp into a small bowl. Place one of the 4 layers of cake onto a cake stand or serving plate. Spread with a quarter of the elderflower cream and a spoonful or so of the passion fruit. Top with the second layer of cake and repeat until you have 4 layers of cake. Spread the remaining cream and passion fruit over the top of the cake and decorate with edible flowers. The cake can be assembled and stored in the fridge for a few hours before serving if necessary.