The panino con bottarga is a Sardinian sandwich organised around one of the most concentrated things in the Mediterranean larder: cured, pressed grey-mullet roe. Bottarga is the egg sac of the grey mullet, salted, pressed, and air-dried until it sets into a firm amber block that is shaved or grated thin. The flavour is intense and saline with a deep iodine edge, the taste of the sea pushed to its limit, more a seasoning than a fish in its own right. The sandwich is defined by that intensity and by the single technique used to make it bearable on bread: shave it thin and round it with fat. A little, handled right, becomes a full sandwich; too much is overwhelming.
The craft is the cut and the counterweight. Bottarga is shaved into translucent slivers or grated fine rather than used in slabs, because its strength is so concentrated that thickness turns it from a flavour into an assault, and thin sheets let it dissolve across the bread instead of sitting as a salt brick. The standard move is butter or good olive oil, spread on the bread or laid under the roe, the fat coating the palate and softening the iodine sharpness so the savoury depth comes through without the harsh edge. The bread is plain, a simple roll or a slice of country loaf, because the bottarga is the entire voice and a flavoured bread would only fight it. Lemon or a thread of oil over the top is the usual extent of any addition. It is assembled close to eating, while the roe is still freshly shaved and the butter has not melted away.
The variations are narrow and stay close to the roe and its fat, and each is its own preparation rather than a footnote here. There is the version with butter alone, the one dressed only in oil and lemon, the one on a harder, drier bread to contrast the unctuous fat. The tuna roe form of bottarga, denser and stronger again, is a different ingredient and follows its own logic, and it deserves its own article rather than being crowded in here.