Chocolate frozen custard with marshmallow swirl

Separate the eggs, passing them between the hands to let the whites slip out; keep any yolk out of the whites. Yolks go in the smaller bowl.

Add the starch, cocoa powder and sugar to the yolks and beat out the lumps.

Loosen with the evaporated milk and beat over low heat as it slowly comes up to a simmer and thickens: first the yolks thicken, then steam appears and the cornstarch thickens.

Keep stirring off the heat to cool it; taste and add a tiny pinch of salt.

Still-freeze: put the custard in the freezer and, whenever it ices up around the edges, beat it to break up ice crystals and distribute the cold. About five stirs over two hours.

When it reaches a cookie-dough texture, whip air into it, then return it to the freezer.

Combine the sugar, corn syrup and just enough water in a pan and bring to a boil.

Sprinkle cream of tartar into the egg whites and beat to peaks, a couple of minutes; beat in the starch until it disappears.

Cook the syrup to 240F (115C), which it reaches only once nearly all the water has boiled off.

Dump the hot syrup into the whites and immediately start beating; it cooks the eggs and gelatinizes the starch.

When cool enough to touch, stir in the vanilla, then freeze, beating before it gets too solid, until cool enough not to melt the custard.

Smash and beat the custard back to a swirlable texture.

Put half the custard and half the meringue into each of two chilled containers and swirl with a spoon handle into thin ribbons, just short of homogenous, with no big chunks of chocolate.

Eat soft, or cover and let harden overnight; let it warm up a few minutes before scooping.