Which nut is used to make marzipan?

Almonds, ground with sugar - and the almond is not a nut. It is the seed inside the stone of a fruit closely related to the peach, which is why an almond in its green husk on the tree looks like a small unripe peach with a shrivelled skin.

Wild almonds are lethal. They contain amygdalin, which releases cyanide when the seed is crushed or chewed, and a few dozen can kill an adult. Domestication turned on a single genetic change switching off that production, and the sweet almond is one of the earlier examples of humans selecting a plant into edibility - deliberately or by finding the one bush that did not poison anyone.

The same compound is why marzipan and almond essence taste of what they taste of, in trace amounts, and why apricot and cherry stones smell faintly similar. Marzipan itself has a contested origin - Persia, Spain and several German cities all claim it - and Lubeck's version has protected status. It became a luxury for the reason most sweet things did: sugar was ruinously expensive, so a paste that was mostly sugar was a way of displaying money at the table.