Rhubarb Shortcake Filling

A simple stovetop rhubarb compote set lightly with gelatine so it holds between layers of shortcake instead of running out. The whole thing takes about fifteen minutes.

• Gelatine quantity2 teaspoons is a little under one standard envelope of powdered gelatine (an envelope is about 2 1/4 teaspoons, or 7 g). Use roughly three-quarters of an envelope; the aim is a soft, spoonable set, not a firm jelly.
• Blooming and dissolvingSprinkle the gelatine over the 1/4 cup cold water and leave it five minutes to swell. The recipe says to add the fruit "to dissolved gelatine" — in practice, stir the hot rhubarb into the bloomed gelatine off the heat, which is what dissolves it. Do not boil the mixture afterwards, as prolonged boiling weakens the set.
• No added liquid for the rhubarbRhubarb and sugar together throw off a great deal of juice within a few minutes over low heat. Start it covered on gentle heat and stir; adding water gives a thin, watery filling the gelatine cannot carry.
• "Soft, but not mushy"This is the hinge. The recipe says only "small pieces"; cut them small and even, and watch the pan rather than the clock, pulling it the moment the pieces yield to a spoon but still hold their shape. Rhubarb collapses to strings very suddenly.
• Red rhubarbThe specification is largely for colour: green-stalked stems cook to a drab brownish filling, while red-stalked or forced stalks give the pink the recipe is after.
• OrangeGrate the zest before juicing, and add the zest at the start with the sugar so its oils cook into the syrup. Half an orange gives roughly 3 tablespoons juice and a teaspoon of zest.
• Rhubarb leavesUse stalks only. The leaf blades contain oxalic acid in quantity and are not eaten; trim and discard them, along with any leaf base still attached.
• Yield and servingMakes roughly 2 cups, enough to fill a shortcake for about six. Used hot it will be loose and saucelike; chilled an hour or more it firms up somewhat, which is the better choice if the shortcake has to stand.