Rhubarb Trifle Glasses

Vanilla pod, split and scraped twice over — once for the rhubarb, once for the cream — is there for more than scent. The seeds carry the flavour; the empty pod, dropped into the simmering rhubarb, still gives something to the liquid as it cooks, which is why you don't throw it away after scraping. If you don't have a pod, a teaspoon of good vanilla extract stirred in at the same point does the job — paste works too, extract from a bottle of "vanilla flavouring" with no actual vanilla in it does not, because there's nothing there to taste.

Rhubarb — go for stalks that are firm and snap rather than bend; a stalk that's gone soft and stringy has lost the acid structure that makes this fruit worth cooking at all. Early-season forced rhubarb is pink and mild; the garden stuff from midsummer is greener, more sour, and will want a touch more sugar. Dice it so pieces are roughly even — not for looks, but so they all soften at the same rate and you don't get spoonfuls that are half mush, half raw fibre.

The water in step 2 is doing almost nothing on its own — a tablespoon is there only to stop the sugar catching before the rhubarb releases its own juice, which it will, generously, within a minute or two of heat. Once it starts simmering you'll see liquid pool at the bottom; that's the sugar and rhubarb's own water doing the work, not the tablespoon.

Rolled oats, not quick oats or jumbo oats — rolled gives you a crumble that toasts evenly and bites with a bit of structure; quick oats turn to dust, jumbo oats stay chewy rather than crisp. Almonds blanched and chopped fine add fat and a bit of bitterness against all that sugar; if you're out, any nut with a mild flavour and some oil in it — hazelnuts, cashews — will stand in, just chop it as fine as the almonds would be.

Toasting the oats and almonds dry, before the butter goes in, matters because butter added too early coats the oats and stops them browning properly — you get soggy-toasted rather than crisp-toasted. You're watching for colour change and smell, not a clock: golden, nutty, and if you catch a whiff of anything bitter or burnt, it's already too late, so pull it off the heat a shade earlier than you think you need to. Butter and sugar melting together afterwards is simple caramelisation acting as glue — it's what turns loose toasted oats into a crumble that holds together in clumps rather than scattering like dust in the glass.

Egg yolks whisked with sugar until "thick and airy" is doing real chemical work — the sugar dissolves into the yolk and the whisking beats in air, and together they thicken the mixture so it can carry its own weight once folded with cream, rather than sinking to the bottom of the glass as a thin yellow puddle. Folding the whipped cream in gently, not stirring, keeps the air you've just beaten into both components instead of knocking it back out — this cream is meant to sit soft and light, not stiff like a piped decoration. Double cream is the right cream here because it's fat enough to hold soft peaks without turning to butter if you overwhip by a few seconds; anything leaner will slump rather than hold shape in the glass.

This serves four properly, or two generously if you've had a big Sunday roast and want pudding that isn't heavy. And the real patience ingredient here isn't the ten minutes of simmering or the five minutes at the stove — it's the cooling. Rush the rhubarb or the crumble into the glass while still warm, and you've made rhubarb crumble soup, not a trifle.