Homemade Tokyo Banana (chiffon sponge wrapped around banana custard)

Thaw frozen overripe bananas in the microwave and drain off the released liquid in a strainer, leaving more starchy banana solids.

Whisk the sugar, cornstarch and salt in a saucepan to remove lumps; off the heat, whisk in the yolks until light, voluminous and ribbony.

Whisk in the heavy cream and a little vanilla, reaching every corner of the pan with a spatula so no yolk mixture is trapped.

Add the mashed banana and blend smooth with an immersion blender, submerged before switching on.

Cook, whisking, until it thickens and holds whisk marks and big bubbles show it is boiling; whisk vigorously about 15 seconds more so the cornstarch is fully activated.

Take off the heat and pass through a strainer.

Press plastic wrap onto the surface to prevent a skin and chill.

Combine the cake flour, salt and baking powder.

Separate the eggs.

Add half the sugar, a pinch of salt and the cream of tartar to the room-temperature whites all at once for a finer foam; beat on low, increasing speed, to stiff peaks without overbeating.

Beat the yolks with the remaining quarter cup sugar until thick and pale.

Stream in the oil as for a sweet mayonnaise, then the vanilla, then on lower speed stream in the milk.

Mix in the dry ingredients on low.

Fold in about a third of the whites with a large flexible spatula until most streaks disappear, then the rest; work quickly before the foam deflates.

Spread thinly, about six or seven millimetres, in a sheet tray, not using all the batter; tap on the counter to pop large bubbles.

Bake quickly, less than 10 minutes, and cool.

Trim the dried edges and invert the sponge onto clean parchment paper.

Shape banana molds by hand from cornstarch and silicone caulk and line them with plastic wrap.

Put the cold custard in a piping bag and cut a roughly three-quarter-inch opening.

Cut rectangles of sponge from the center, avoiding wrinkles, smooth side out; spritz with water if dry.

Press a piece of sponge into the mold, pipe in custard, and fit a trimmed bottom piece inside the rounded layer.

Wrap tightly in the plastic so pressure and moisture make it adhere; chill a little over an hour, about an hour 15.