Double cream

Double cream is the richest of Britain's pourable creams — a full-fat grade fixed by UK dairy law at a minimum of 48% milkfat, so nearly half its weight is pure butterfat. That extraordinary fat load makes it spoonably thick straight from the pot, whips to stiff peaks in seconds, and leaves so little of the casein protein that would otherwise clump that it can be boiled hard into a sauce without curdling. Only clotted cream sits above it on the scale.