Cypriot Easter Bread (flaounes)

To make the filling, combine the cheeses, yeast mixture, semolina, plain flour and eggs in a large bowl. Cover and refrigerate overnight. The following day, stir in the mint, baking powder and sultanas until well combined.
To make the pastry, place the flour, mastic, mahlepi, yeast mixture, butter and salt in a large bowl.
Adding the milk a little at a time, knead ingredients together until soft but not sticky. Cover with plastic wrap, a towel or blanket, and set aside to rest for 1 hour.
Meanwhile, to make the glaze, place the sesame seeds, vinegar and enough water to cover in a small saucepan and bring to boil. Drain well and spread seeds over a tea towel to dry.
To assemble, divide dough into large pieces and roll out on a lightly floured work surface until about 3 mm thick. Using a saucer as a template, cut into 18 cm rounds.
Preheat the oven to 180°C. Line baking trays with baking paper. Firmly press one side of pastry rounds into sesame seeds on tea towel to coat bases well. Place 1 heaped tbsp of filling into centre and fold in three sides to make a rounded triangle shape, leaving a gap in centre with filling exposed.
Place on prepared trays. Brush tops with beaten egg yolk and bake for 30 minutes, or until golden.