sulguni cheese
A Georgian brined cheese made from cow's or buffalo milk, scalded and kneaded like mozzarella, sliceable, salty and mildly sour.
Sulguni is a pasta filata cheese from western Georgia that is stretched and kneaded in hot water after souring and then matured in brine. It is firmer than fresh mozzarella, with a fibrous texture that peels apart in layers, and tastes distinctly salty with a milky, slightly sour note. When heated it melts into long, elastic strands without releasing much fat, which is why it is prized for baked and filled breads. A smoked version also exists, with a yellowish rind and a smoky aroma. It can be found in Russian and Eastern European grocery shops, occasionally in Georgian stores, and through chilled mail order.
Substitute:
The usual stand-in is roughly two parts low-moisture mozzarella to one part feta or another brined cheese: the mozzarella provides the melt and stretch, the feta the salt and tang. The blend does not fully match sulguni, being softer and less fibrous, and feta on its own would crumble rather than melt. For smoked sulguni, part of the mix can be replaced with smoked scamorza.