Green Colouring Butter

Beurre colorant vert (green colouring butter) teaches one precise thing: the useful colour is caught in the coagulated solid, not left swimming in the vegetable water. Extract the raw spinach juice, warm it gently in a bain-marie (hot-water bath), and the pigment-rich matter gathers into deep green flecks that can be drained and preserved in butter.

The original formula assumed a saucier with time to pick and pound two pounds of spinach, a strong serviette for wringing, a mortar, and a broad tammy for finishing a service quantity. Here the spinach is halved to a manageable home batch, the pounding is done in a food processor, and a flour-sack towel and fine-mesh sieve replace the professional cloth and tammy. Those are brigade scaffolding. Extracting the raw juice, coagulating it gently, draining it thoroughly, and adding butter at exactly half the colouring matter's weight are the dish, and they stay untouched. One cook, one stove, one evening.

The finished butter should be intensely emerald, smooth enough to disappear into a pale sauce, and nearly neutral in taste. Control the bain-marie above all: it must warm the juice until green curds form, never boil it into khaki submission.