This charlotte is built upside down offering flawless results. It is layered with a luscious vanilla creme diplomate and a wild blueberry marmalade insert that fit the shape of the muffin cake bottom. The crown is the ladyfingers.
Yields a 8X3-inch/20X7.5 cm charlotte ring. Make a day or two ahead.
Bring slowly to a boil, frozen blueberries with sugar and lemon juice or citric acid (Citric acid is a naturally occurring antioxidant). Turn off the heat, cover and let sit for a couple of hours or best overnight. Sieve and save solids and juice for the insert and simple syrup.
Soak gelatin in cold water to soften and drain. Bring to boil blueberry solids with the juice and sugar. Add fresh blueberries – bring to a boil and remove from the heat. Stir in the soften gelatin and mold out into a ≈7-inch/18 cm diameter pastry ring (tight up bottom ring with plastic wrap). Let cool and freeze.
Soak gelatin in cold water to soften, and drain. Gelatin in syrup remains optional. Though, it is often used to prevent syrup from oozing out from the sponges once the cake is put on display. Bring to a boil blueberry juice with water and sugar. Remove from the heat, add gelatin. Use syrup when lukewarm or at room temp.
Draw a couple of 3.5-inch/9cm lines on parchment paper. Lightly oil a large baking tray and stick parchment on it (Place it upside down, so the ink is never in direct contact with the food). Sift flour and set aside. In the stand mixer fitted with the whisk attachment, beat egg whites with cream of tartar and one-third of the sugar on medium speed. Always allow egg whites to incorporate as much air as possible before turning into meringue. Meanwhile, turn oven on and increase mixer speed to high. Turn oven on to 375ºF/190ºC. Lower oven temperature to 350ºF/180ºC if using a convection oven. Continue beating until stiff peaks adding remaining sugar gradually. Lower mixer speed and add egg yolks. As soon as they are incorporated, stop mixer and fold in the sifted flour with a spider skimmer or spatula. Pipe out 3.5-inch length ladyfingers using a large plain pastry tip #809. Dust ladyfingers with a mixture of one to one ratio to powdered sugar and corn starch (≈2X15g). Repeat once.
Bake ladyfingers for about 18 minutes. Once baked, slide ladyfingers over the countertop. Let cool and carefully remove from the parchment.
Sift flour and baking powder together; set aside. In the stand mixer fitted with the whisk attachment, beat together eggs with sugar and salt on high speed. Add the oil, mascarpone and milk. Then add the sifted powders. Transfer batter to the greased cake ring and bake at 350ºF/180ºC for 25 minutes. Transfer cake to a cooling rack and let coo. Refrigerate prior to cut.
Place a baking tray lined with plastic wrap in the freezer. Soak gelatin in cold water to soften; drain and set aside. Make a pastry cream first. In a medium size saucepan, bring milk, vanilla and a third of the sugars to a boil. Turn the heat off, cover and let infuse for 20 min or so. Meanwhile, beat egg yolks with the remaining sugar, and add starches. Temper yolk mixture with a third of the hot milk, then add remaining liquid, and transfer mixture back to the saucepan mixing swiftly. Bring to a boil, and cook custard for 2 minutes whisking constantly. Add white chocolate and mix well until chocolate is incorporated. Turn off the heat, add softened gelatin and mascarpone. Blend custard with an immersion blender. Transfer custard onto the frozen baking tray. Cover custard with plastic wrap in contact and top with an ice pack and refrigerate.
Trim muffin cake top off and make one or 2 more disks that should be about half inch/1.25 cm thick. Make sure to keep the bottom of the muffin cake thick enough. It should indeed measure an inch/2.5 cm tall. Trim one of the disk into a 7-inch/18 cm round. Save scraps for snacks...
To seal the bottom of the charlotte ring tightly with plastic wrap, moisturize it with a wet sponge. Place cake ring onto a plater. In the chilled mixing bowl, whip heavy cream to medium peaks. Transfer whipped cream to a container. Re-use the same mixing bowl and beat the chilled custard. Fold whipped cream into the custard.
Fill the prepared charlotte ring with 80% of the diplomate cream. With a tablespoon, spread some of the filling to cover all sides around the cake ring. Place the 7-inch muffin cake disk and moisturize it with some of the blueberry simple syrup. Do likewise with the thick muffin cake bottom. Add remaining diplomate cream and top with the frozen blueberry insert.
Enclose cake ring and place in the freezer for at least 5 hours prior to unmold. At this juncture, the cake can be kept frozen for up to 2 months for later events.
Warm up cake ring using your hair dryer to demold it and refrigerate. Meanwhile, trim off ladyfinger bottoms into 3-inch/7.5 cm tall cookies. Save trimmings for later use. Arrange ladyfingers all around the cake and place in the refrigerator overnight. The cake must be completely thawed before eating. Top charlotte with blueberries and drizzle over the remaining syrup. Enjoy!