Coffee Mousse

A still-frozen gelatine mousse from the era when the electric refrigerator was new enough to be named in the instructions. The technique is sound, but the freezing hardware has changed more than the recipe has.

• The freezer is the hinge"Trays of electric refrigerator" almost certainly means the ice-cube trays in the small freezing compartment, which ran considerably warmer than a modern freezer's 0F. A modern freezer will set this harder than intended; move it to the refrigerator for 20-30 minutes before serving so it slices soft.
• Gelatine quantityOne tablespoon is about 1 1/3 envelopes of modern powdered gelatine, or 9-10 g. Use a level tablespoon, not heaped, or the mousse turns rubbery rather than creamy.
• Blooming and dissolvingGive the gelatine a full five minutes in the cold coffee before adding the hot. The hot coffee should be near boiling to dissolve it completely, but the mixture must then be cooled to barely warm before it meets the cream, or it will deflate the whip.
• Folding, not stirring"Add slowly" means fold in a thin stream while the whisk keeps moving, or in three additions. Coffee poured in at once will collapse the cream and give a grainy, layered set.
• Powdered sugarMost likely confectioners' sugar, though in older American usage the term could also mean finely ground granulated. Either dissolves readily into the whipped cream; if using granulated, dissolve it in the hot coffee instead.
• The coffee itself"Strong clear coffee" means brewed strong and free of grounds, not espresso. The frozen mixture mutes flavour noticeably, so brew it about half again as strong as you would drink it.
• CreamTwo cups of heavy cream, whipped stiff but stopped before it goes buttery. The folded mixture makes a generous quantity; divide it between whatever shallow trays or a loaf pan you have.
• Yield and holdingEight servings, as stated. It keeps a week covered in the freezer, though it picks up freezer odours readily; press plastic wrap onto the surface.