In a blender bowl, blend the flour, salt, and butter until it becomes a crumbly mixture.
Add the egg and water. Continue to blend until the dough starts to unify.
Shape the dough into a disc-shape on baking paper and put it in the refrigerator to rest for 30 minutes.
Heat the oven to 180°C / 350°F with the fan.
In a mixing bowl, mix the mozzarella and finely chopped tomato.
Take the dough out of the refrigerator and roll it out on a floured surface.
Use a glass or a round cookie cutter to cut circles out of the dough.
Fill each dough circle with 1 teaspoon of filling and close the dough into triangular-shaped cookies.
Add olives or the other flavor you are using.
Place the cookies on a baking tray.
Bake for 9-10 minutes.
Cool at room temperature.
Have a hamantaschen and Happy Purim!