Preheat the oven to 390°F (200°C). Sift flour and potato starch in a large bowl and set aside.

Rolled biscuit batter: Separate the egg whites from the egg 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 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 spatula.

Divide the batter into two parts. Spread the first part of the batter on a 12 x 16 inches (30 x 40 cm) baking sheet covered with parchment paper to the thickness of 1/5 inches (5 mm) and smooth with a bent spatula. Alternatively, use a non-spill baking sheet (no need to grease it). 

Bake for 10 minutes. Once the biscuit is ready, remove it from the oven and cover it with a clean tea towel. Flip it on top of the cloth and carefully remove the parchment or silicone sheet: gently lift the corners and then the mat or paper's whole surface. Cover the biscuit with another parchment layer and roll it from the long side to let it cool and keep the moisture. Repeat the same with the second part of the cake batter.

Unwrap the cooled cake. Spread a thin layer of the raspberry jam and roll it into a tight spiral with parchment paper. Wrap the rolled biscuit in plastic film and refrigerate for about three to four hours to facilitate cutting.

Cream Anglaise: Place gelatin sheets in a bowl of cold water and let it soak 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 yolk mixture back to a saucepan, cook over low heat, and continue whisking. Once the custard coats the back of the spoon and reaches 179°F (82°C) - use a sugar thermometer - and take the pot from the heat. Add the drained gelatin. Transfer the custard to another bowl, cover it with plastic wrap in contact, and let it cool to room temperature.

Bavarian cream: Pour heavy cream into the bowl of a stand mixer with a whip attachment (you can use an electric mixer) and whisk cream until soft peaks. Add the whipped cream to the cooled custard, gently mixing with a wooden spoon or spatula. Let it rest to thicken slightly, occasionally stirring.

Assemble Charlotte: Line the bottom and sides of a bowl 8 inches (20 cm) in diameter with a plastic film. Cut the edges of the sponges with a sharp knife, then cut rolled biscuit into thin slices - 5 mm or 1/5 inch thick. Arrange them at the bottom and sides of the lined bowl, pressing them against each other and the dish. 

Fill with Bavarian cream: 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, and place a plastic film on top of the biscuits.

Finish cake assembling: Place a cardboard base over the top of the bowl to pack everything. Refrigerate the Charlotte cake for at least 6 hours and up to 24 hours. When ready to serve, remove the cardboard and plastic, flip the cake on a serving plate, lift off the bowl, and serve immediately.