Caramel sauce:

1. Melt the sugar in a heavy-bottomed saucepan with the water until it is brown and liquid. Add the melted butter and cream.
2. Stir the flour into the milk and add to the caramel mixture. Bring to a boil and stir until it has a thick consistency. Remove from the heat and let cool. It should be refrigerator cold when you spread it on the cake.

Cake:

1. Preheat the oven to 200 degrees.
2. Beat the eggs and sugar until thick. Sift in the flour and baking powder. Fold in carefully with a spatula and spread the mixture onto a baking paper-lined baking sheet.
3. Bake in the middle of the oven for 8-10 minutes.
4. Invert the cake onto a sugared kitchen towel and remove the paper. Place the baking sheet over the cake until it has cooled.

Filling and assembly:

1. Whip the cream and vanilla sugar until creamy. Spread this over 2/3 of the cake.
2. Roll up the cake and place it on a plate, seam side down. Spread the remaining cream over the cake, then spread the caramel sauce over it.