For the sponge cake, line a baking tray (approx. 35 x 40 cm) with baking paper. Preheat the oven (electric cooker: 200°C/circulating air: 175°C/gas: level 3). Separate the eggs. Beat the egg whites and 3 tbsp. cold water until stiff, adding 100 g sugar.
Stir in the egg yolk. Sift flour, starch and baking powder over it and fold in. Spread the sponge cake mixture on the baking tray. Bake in a hot oven for 8-10 minutes.
In the meantime, soak the gelatine in cold water for at least 5 minutes. Sprinkle a clean, damp tea towel with 2 tbsp. sugar. Turn the sponge cake plate over onto the cloth immediately. Moisten the baking paper with water and remove carefully immediately.
Roll up the biscuit from the long side using the cloth.
Mix quark, coconut milk, rum, lemon juice and 3 tablespoons of sugar. Squeeze the gelatine, dissolve at very low heat. First mix with 2 tbsp. coconut quark, then stir into the remaining quark. Chill for 10-20 minutes until the cream begins to gel.
Drain the pineapple and chop finely. Whip the cream until stiff and pour in 3 tbsp. sugar. Fold the cream into the coconut quark and put 5-6 tbsp aside for spreading. Fold the pineapple into the remaining coconut cream.
Unroll sponge roll and spread with pineapple-coconut cream, leaving 4-5 cm free at the top. Roll up the roll from the other end. Spread with the remaining coconut cream and sprinkle with coconut flakes.
Put the sponge roll in a cool place for 3-4 hours.