The key ingredient is Bulgarian white cheese, called sirene. It is similar to feta cheese - salty, crumbly and slightly tangy. Mixed with beaten eggs it makes a creamy, savoury filling that puffs up inside the crispy pastry layers as it bakes. The smell of banitsa coming out of the oven is one that Bulgarians remember forever.
Making banitsa is a real skill. The filo dough is stretched until it is paper-thin - you should almost be able to read a newspaper through it. Butter or oil is brushed between each layer to keep them separate and crispy. Layering and rolling filo dough without tearing it takes practice and patience.
There are many variations of banitsa. Some are filled with spinach instead of cheese, some with pumpkin and sugar for a sweet version, and some with leeks. On New Year's Eve, bakers tuck a lucky charm inside the pastry before baking - traditionally a small coin, or a piece of cornel wood. Whoever finds the charm in their slice will have good luck in the coming year.
Banitsa is sold everywhere in Bulgaria: in bakeries that open at five in the morning, at market stalls, in school canteens and at petrol stations. A warm banitsa with a cup of cold ayran yogurt drink is the classic Bulgarian breakfast on the go.