Floating islands are similar to snow eggs but are baked in the oven in a bain-marie (water bath). The dessert can be made in individual portions, as here, or in a large soufflé mold.
The bottom of each mold is coated with a caramel finished with butter to keep it a bit softer. The filled molds are then cooked, surrounded by water, in a roasting pan. Some of the caramel adheres to the bottom of the dishes when the floating islands are unmolded, but some of it drips down over the desserts to mix with the custard sauce.
The rum-custard sauce is made with fewer egg yolks than traditionally called for in a custard cream. The milk, cornstarch, and sugar mixture is brought to a rolling boil and poured directly on top of the yolks. Because of the small proportion of egg yolks to milk, the temperature of the mixture rises to 180 degrees, ensuring that the lecithin in the egg yolks wil thicken. The sauce doesn't need further cooking and is strained to eliminate any curdled pieces. Here the custard sauce is flavored with rum, but it could be flavored with cognac, bourbon or vanilla instead.
Floating islands can be cooked a day or so ahead and kept, covered, in the refrigerator so the tops don't get rubbery. Covering also keeps the dessert moist, preventing the sugar from hardening around the edge of the molds, and thus making the floating islands easier to unmold.
Spoon 3 to 4 tablespoons of rum-custard sauce onto individual serving plates, and unmold the small floating islands on top, letting whatever caramel that comes out drip over them. Decorate with some extra toasted almond slices, and serve immediately.
