I'm giving this recipe at the insistence of my friend Linda, who remembers it from my time as pastry chef of The American Pie, a now-closed restaurant in Lan Kwai Fong that was famous for its desserts.
Biscuits à la cuillère are also known as ladyfinger biscuits, but don't even think of using the crisp, commercially made ones. Home-made ladyfingers are delicate, soft and spongy.
Chocolate banana charlotte
For this charlotte, you'll need a springform cake pan that is 18cm in diameter, or an 18cm cake ring that is 6cm in height, set on a completely flat serving dish.
Biscuits à la cuillère
4 large eggs, at room temperature, separated
155 grams granulated sugar, divided
½ tsp baking powder
1 tsp vanilla extract
¼ tsp cream of tartar
¼ tsp fine sea salt
125 grams pastry flour (or use 100 grams plain [all-purpose] flour mixed with 25 grams of sifted cake flour)
Icing sugar, for dusting
Preheat the oven to 180 degrees Celsius. Use a marker pen to trace an 18cm circle onto a sheet of parchment paper, then flip the sheet of paper over so the inked side is face down and place it on a baking tray - the circle is the base of the charlotte. Use the marker pen and a ruler to draw a straight line that's the length of a baking tray on a sheet of parchment. Draw a second line 6cm away from, and parallel to, the first. Draw two more parallel lines of the same dimension on the same sheet of parchment, separated from the first set by at least 2cm. If necessary, you'll need to draw additional sets of parallel lines - this depends on the length of your baking tray. The total length of the 6cm-high parallel lines needs to be at least 57cm (remember pi?) to make the perimeter of the charlotte. Flip the sheet of parchment over so the inked side is face down and place it on a baking tray. Prepare a piping bag fitted with an 8mm plain tip. Put the icing sugar in a fine sieve.
Separate the eggs: put the yolks into a large bowl and the whites into a medium-sized one.
Use an electric beater fitted with the whisk attachment to beat the yolks. Add 90 grams of sugar, the baking powder and the vanilla and beat until the ingredients are thick and pale yellow. Remove the whisk attachment from the electric beater, wash it in hot, soapy water, then dry it and fit it back on the beater.
Use the beater to whisk the egg whites until frothy. Whisk in the cream of tartar and salt. With the beater speed on medium, add 65 grams of sugar in a slow, steady stream. Whisk the egg whites on high until the mixture forms soft peaks. Set the bowl aside.
Working quickly (because the whipped whites won't maintain their volume for long), use the electric beater (no need to wash the whisk) to beat the flour into the egg yolk mixture until smooth. Scrape the mixture from the whisk attachment. Add one-third of the whipped egg whites into the bowl holding the yolks. Use a rubber spatula to quickly combine the ingredients until smooth. Add half of the remaining whites to the bowl and gently fold them into the mixture, maintaining as much volume as possible. Add the rest of the whites and gently fold them in. Put as much of the mixture as possible into the piping bag. Starting at the centre of the traced 18cm circle, start piping the mixture in continuous, concentric circles to make the base of the charlotte. On the tray with the lines, pipe the ladyfingers 6cm high in a continuous, up and down motion, along the length of each strip. Any leftover batter can be piped into individual-size biscuits. Lightly dust the piped shapes with icing sugar, then bake at 180 degrees until fragrant and pale golden; when you touch the surface, it will spring back. Cool completely.
To make the chocolate mousse
Once the mousse is made, you'll need to assemble the charlotte quickly, or the mousse will harden.
4 egg yolks
200 grams bittersweet chocolate (with a cacao content between 60 and 75 per cent), chopped
100ml cream, chilled
20 grams granulated sugar
5 grams gelatin sheets
Place the chocolate in a clean, dry bowl and set it over a pan of barely simmering water. Heat, stirring often, until the chocolate is melted. Put the gelatin sheets in a pan of cold water and leave until they're soft. Drain off the water and squeeze the liquid out of the gelatin. Put the gelatin in a small bowl with the rum. Melt the gelatin by placing the bowl in a larger bowl holding about 1cm (in depth) of very hot water. Stir the gelatin until it is smooth and warm, then whisk it into the warm melted chocolate. Mix in the yolks. Leave at room temperature until tepid, whisking often. Whip the cream with the sugar until the cream forms soft peaks, and quickly fold it into the chocolate.
To assemble and finish the charlotte:
50 grams granulated sugar
20ml dark rum
10-12 ripe Thai bananas (use small ones that are about 10cm long)
75 grams bittersweet chocolate (with a cacao content between 60 and 75 per cent), chopped
Melt the sugar in 50ml of hot water, then stir in the rum. Carefully peel the charlotte base (the circle) from the parchment paper and put it into the springform pan (or cake ring); if necessary, trim the charlotte base so it fits. Use a pastry brush to spread some of the rum syrup evenly over the base. Peel the sides of the charlotte - the 6cm-high lengths of piped biscuit - from the parchment and turn them over so the piped-side is down. Brush them with the rum syrup then fit them into the ring, trimming them to fit; the piped-side should be facing outward. Spread a thin layer of mousse over the charlotte base. Peel the bananas and put five or six of them close together (but not touching) into the ring then add more mousse to cover the bananas by about 1cm. Firmly tap the pan so the mousse fills any holes. Put more bananas over the first layer then add more mousse until it comes within 5mm of the top of the charlotte. Refrigerate for several hours. (Leftover mousse can be put into small bowls, to serve separately.)
Make the ganache. Heat the cream until simmering then pour it over the chocolate and whisk until smooth. Spread a thin, even layer of the ganache over the mousse and refrigerate until set. Remove the outside of the springform pan (or the cake ring) from the charlotte just before serving.