There's no sauce involved at all — the wrap is bound only with butter, chopped pickles, and dried mint, and it's meant to be eaten dry.
Boiled potatoes and eggs are mashed together with butter, chopped pickles, salt, and dried mint, then rolled up in a sheet of thin lavash bread. Cart vendors across Iranian Azerbaijan, from Tabriz to Urmia, sell it as a cheap, fast lunch.
Why it's made this way: Its Azeri Turkish name — yer alma (potato) and yumurta (egg) — marks it as a product of the region's Turkic linguistic heritage, distinct from the Persian-named street snacks found elsewhere in Iran.