Lemon-Cream roll

This sponge cake filled with whipping cream and lemon is a refreshing summer dessert. Although many people's favorite and frequently found in German bakeries, some practice is required when making it.
Although I've made many cakes with sponge cake I've never attempted a roll, so this is an exciting experience for me from which I will certainly learn something.

Ingredients:

a baking sheet (40 x 30 cm) lined with parchment paper
a towel or second sheet of parchment paper generously sprinkled with sugar (the sugar prevents the sponge cake from sticking to the towel or paper)
a small stove-top pot or casserole

Sponge cake:
4 eggs
1 egg yolk
1 package vanilla sugar or some vanilla aroma
80 g sugar
80 g wheat flour
1/2 teaspoon baking powder

Filling:
2/3 of a package of gelatine powder
4 tablespoons lemon juice
zest of one lemon
70 g confectioner's sugar, sifted
400 g cold whipping cream


1. Preparation: Grease baking sheet and line with parchment paper. Fold parchment papers along edges to form edges. Preheat oven to 200°C (375F)
2. Sponge Cake: Mix eggs and egg yolk with a hand mixer on highest setting until foamy (about 1 min). Mix sugar and vanilla sugar or vanilla aroma, and add slowly to eggs while beating the eggs, then keep beating the batter for an additional 2 min. Mix flour and baking powder, and briefly mix with batter. Evenly flatten batter on baking sheet. Bake for about 10 min in the middle of the oven until golden brown.
Remove sponge cake from oven and put upside down on sugar-sprinkled towel or parchment paper. Remove baked parchment paper, and immediately roll the towel and the sponge cake from the longer side to form a roll. Rolling the cake before it cools down prevents the sponge cake from breaking.
3. While the sponge cake is cooling, prepare the filling. Add 2/3 of a pack of gelatine and 2 tablespoons of water to a stove-top pot. Beat whipping cream until almost stiff. Heat gelatine on low heat setting until it dissolves, then mix in lemon juice, lemon zest, and sifted confectioner's sugar. Now dissolve 2 tablespoons of whipping cream in the gelatine, then immediately add the gelatine mixture to the whipping cream and beat until fully stiff.
4. Unroll the sponge cake. Evenly add the cream mixture onto the sponge cake, and roll from the longer edge back up. Chill lemon-cream roll for at least 2 h in refrigerator before serving.
5. Decoration: Sift confectioner's sugar over roll before cutting and serving.