Clean and wash the greens.
In a deep frying pan, heat a bit of oil and sauté the onions until translucent. Then add the greens to wilt and reduce in volume.
Add the herbs, salt, and freshly ground pepper at the end.
Remove from heat and let the mixture cool down.
Beat the eggs, add them to the greens mixture and then add the crumbled feta cheese.
In a bowl or mixer, mix the gluten-free flour, salt and baking soda (or sparkling water) thoroughly.
Let the dough rest and then roll it out into a thin sheet.
Spread the butter on the dough.
Cut the dough vertically into 4-5 strips and place one strip on top of the other. Then cut the strips in half.
Chill the dough in the refrigerator until the butter is absorbed, then open the pieces like a book into two layers.
Place one sheet of dough in a baking dish, add the filling and cover it with the second sheet of dough.
If desired, sprinkle with sesame seeds.
Bake at 180°C (356°F) on the upper rack for about one hour.
The dough can be prepared in advance from the previous day and kept in the refrigerator.
The same filling can be used to make a pie with ready-made dough.