# Pour the warm milk
into a deep bowl and yeast in it. Mix the mixture by fingertips.
# Add egg, egg white, vegetable oil and salt in it. Mix it for a while more.
# Knead the mixture by adding flour
little by little, until the mixture turns into soft dough. The dough should not stick to your hands.
# Cover the dough. Rest it at room temperature for about 45-60 minutes.
# Meanwhile, prepare the filling mixture. Dice the onion
thinly, knead it with salt, and then transfer into a pot. Add thinly cut spinach
and oil on it and mix.
# Cover the lid of the pot. Place the pot over low heat. Cook it for about 20 minutes without uncovering its lid.
# After cooling down the spinach
mixture, add chipped cheese
# Divide the rested dough into 20 equal pieces. Roll out each piece over the flour
ed bench by a rolling pin in oval shape. Each piece should have 1 hand span length and 4 fingers width.
# Place enough filling mixture onto the wide side of the rolled out dough. Firstly, roll it and then get the both ends together to shape it as a croissant.
# Place the croissants into a baking tray with spaces between them. Rest them in the tray for about 20 minutes.
# Then, spread egg yolk all over. Sprinkle nigella and sesame all over.
# Place the tray into the oven which is preheated to 375 F. Bake the croissants until they turn into red.
# It is advised to serve warm.