Sift the flour into a large bowl, add the salt, and mix. Make a well in the center and add the dry yeast and sugar. Pour in the warm milk to dissolve the yeast and mix.

Add the vegetable oil and egg white, kneading until the dough is soft and non-sticky. Cover and let rise for 30 minutes.

Prepare the filling by mixing the cheese and chopped spinach in a bowl. Add black pepper if desired.

Take walnut-sized pieces of dough, shape into balls, and flatten. Add the filling to the center, fold into a half-moon shape, and seal.

Place on a parchment-lined baking tray and brush with egg yolk. Bake in a preheated oven at 180°C (350°F) for 20-25 minutes.

Serve warm or at room temperature.