What is zybac?

Answer 1

Perhaps you mean 'zwieback', rather than 'zybac'?

Zwieback is bread, made with eggs, baked and thinly-sliced: the slices are oven-baked to achieve a thin, crisp toast-like biscuit in the sense of a Melba toast type of cracker.

Often sold as baby rusks, or as crackers, zwiebacks are used as appetisers with toppings and dips, and there are many recipes for flans and crumble-type dishes using zwieback crumbs.

The word 'zwieback' is from German - zwei (twice) + backen (to bake), so twice-baked. Incidentally, biscuit in French, and biscotti in Italian, have a similar origin: twice + cooked.