Step 1

Preheat oven to 390 F/200 C.

Step 2

To make the rolled biscuit, sift flour, and potato starch in a large bowl and set aside. Separate the whites from the yolks with an egg separator. Beat the whites at medium speed, gradually adding sugar. Once the meringue is glossy, decrease the mixer speed and add egg yolks whisked as for an omelet. Beat the mixture for the other 15 seconds till all the ingredients are well incorporated. Add the sifted dry ingredients and gently mix with a rubber spatula.

Step 3

Divide the dough into two parts. Spread the first part of the dough on a Lekue 12 by 16-inch/30 x 40 cm non-spill baking sheet (no need to grease it) or a baking sheet covered with parchment paper up to the thickness of  5 mm, smooth with a bent spatula, and bake for 10 minutes. Once the biscuit is ready, take it out of the oven and cover it with a tea towel. Flip it on top of the cloth and carefully remove the silicone sheet or parchment: gently lift the corners and then the mat or paper's whole surface. Cover the biscuit with another parchment layer and roll it in to let cool and keep the moisture. Repeat the same with the second part of the biscuit dough.

Step 4

When the biscuit is cooled, unwrap it. Spread a thin layer of the raspberry jam and roll tightly with the help of parchment. Wrap the rolled biscuit in a plastic film and refrigerate for about three to four hours to facilitate cutting.

Step 5

soak gelatin sheets in cold water for 10 minutes. Bring whole milk with the scraped vanilla seeds to a boil. In a separate bowl, whisk egg yolks with sugar, then pour in the hot milk slowly while continually stirring. Bring the mixture back to a saucepan and heat over low, and continue whisking. Once the custard starts thickening, take the pot out of the heat and add the drained gelatin. Transfer the custard to another bowl, let it cool, stirring occasionally.

Step 6

Once the custard has cooled, whisk whipping cream until soft peaks and add to the cold custard. Gently mix with the spatula. Let it rest to thicken slightly, stirring occasionally.

Step 7

line the bottom and sides of a bowl eight inches/20 cm in diameter with a plastic film. Cut the rolled biscuit into 5 mm thick slices and arrange them at the bottom and sides of the bowl, pressing them against each other and the dish. Pour a third of the Bavarian cream in the center and distribute half of the fresh raspberries. Pour another third of the cream again and repeat the layer of raspberries. Finish with the cream. Cover the bottom of the bowl with the remaining rolled biscuit slices, place a plastic film on top of the biscuits. Also, cover it with a cardboard base to pack everything additionally. Refrigerate the Charlotte cake for at least 6 hours and up to 24 hours.

Step 8

When ready to serve, remove the cardboard and plastic, flip the cake on a serving plate, lift off the bowl, and serve immediately. Or brush the cake with a thin layer of a cake glaze or a neutral topping and refrigerate until serving.