Make the papaya purée first. Halve the papaya lengthwise and remove the seeds with a spoon. Remove the skin and slice the flesh into 1.5 cm pieces.
Weigh 500 grams of flesh (save the rest). and place in a pan with 200 ml of water. Bring to the boil then leave the mixture to simmer gently for 5 minutes. Blend into a smooth purée with the hand blender. Add the jam sugar and cook for 5 minutes. Allow to cool in the refrigerator.
Preheat the oven to 120 °C C. Line the baking tray with baking paper.
To make the cake batter, place the eggs, caster sugar and the vanilla extract in an heat-proof bowl. Place the bowl over a pan with a layer of boiling water (au bain-marie). Do not let the bowl touch the water! Beat the batter with the mixer in approx. 5 mins. until pale yellow and airy. Continue to beat the eggs until the sugar crystals have completely dissolved.
Remove the bowl from the heat and beat for another few minutes. Sieve the flour, cornflour and 1 pinch of salt above the creamed mixture. Gently fold the dry ingredients through the batter. Spread the batter in an even layer in the baking tray. Bake the cake for 15 minutes. Leave to cool on a wire rack for 2 hours.
For the filling, zest the peel of 1 lime. Squeeze the juice. Whip the cream with the mixer until stiff. Beat the mascarpone until light and airy. Adde lime juice, zest and icing sugar. Fold the whipped cream through this mixture as lightly as possible.
Cut the rest of the papaya flesh into 5 mm cubes. Turn out the cooled cake on a sheet of baking paper. Gently peel off the other sheet of baking paper. Brush the cake with the papaya purée , but leave a 2 cm gap on the long side of the cake. Cover the purée with lime cream and sprinkle with the cubed papaya. Reserve some of the cream and papaya as a garnish.
Carefully roll up the cake from the long edge. Place on a serving dish with the open edge underneath to keep it tightly rolled. Garnish with the lime cream, cubed papaya and some extra lime slices.
