Preheat the oven to 100°C and line a tray with baking paper.
Boil fennel with sugar and 100ml water, then simmer until soft and syrupy.
Bake half the fennel for 1 to 2 hours at 100°C.
Preheat the oven to 180°C and line a 20cm springform cake tin.
Layer the remaining fennel at the base of the prepared cake tin.
Melt the chocolate and butter together in a heatproof bowl over simmering water.
Whisk egg yolks with two tablespoons of sugar and stir in the chocolate.
Whisk egg whites with remaining sugar until stiff peaks form.
Fold egg whites into the chocolate mixture and pour into the tin.
Bake at 180°C for 20 minutes then leave to cool.
Whisk double cream until stiff, then mix in cream cheese and passion fruit.
Serve cake wedges dusted with cocoa, topped with candied fennel and cream.