Put the flour, yeast, sugar, egg, oil, and salt into a mixing bowl (making sure to keep the salt away from the yeast).

Mix, while adding the water gradually.

Knead until the mixture is soft and uniform.

Oil the dough. Cover and let rise for an hour, until it doubles in volume.

Preheat the oven to 350°F (180°C).

Melt the butter in a frying pan.

Sauté onion until golden.

Add mushrooms and sauté for about five minutes. Remove pan from the flame.

Strain the liquid from the mixture. Mix in the grated cheese and salt.

Divide the dough into four equal balls.

On a floured surface, roll each ball into a flat circle. Divide each circle into seven triangles.

Place a tablespoon of the filling at the wider side of the triangle. Form a croissant by rolling the dough over the filling toward the narrower end.

Place the croissants on a baking tray lined with Gefen Parchment Paper. Brush the croissants with egg wash and sprinkle black sesame seeds or poppy seeds over them.

Bake for about 20 minutes, until golden.