Preheat oven to 400°F (200°C).
Combine the salt and flour.
Cut the butter into cubes and add to the flour mix.
Using your fingers, mix the butter into the flour mixture until it's combined.
Add the water slowly until you form a dough. Refrigerate for 10 minutes.
Roll out on a floured surface. Fold the dough in thirds and roll again. Continue this process several times.
Roll out one final time. Using a cookie cutter, cut out 16 circles.
Finely chop the cheeses and mix in a bowl with zaatar.
Place a spoonful of the cheese filling in each circle.
Whisk the egg in a small bowl and use this to seal the circles into half moon shapes.
Place on a tray and glaze with the remaining egg. Chill in the fridge until firm.
Bake for 15 minutes, or until brown.