In a bowl, add the flour, salt, butter, and rub the ingredients between your hands or the tip of your fingers. You can also use a fork. Add the chilled water and mix for few seconds. After mixing well, you should get a wet sand-like texture.

Bring the dough together and form into a disk. Wrap with a plastic wrap and refrigerate for at least 30 minutes.

In a small pan, add the olive oil and butter. Add the onion and sauté until the onion is light brown.

Add the spices and mix well. Cook on medium low for two minutes.

Let the mixture cool to room temperature.

Preheat the oven to 400F/220C. Place a parchment paper on your baking sheet. Keep aside.

Lightly dust your working surface with flour. Place the dough on your working surface and roll out to 6 or 7 inches.

Place the cheese in the middle of the rolled dough and place the mushroom and onion filling on top.

Fold the dough edges, up and to the center, do this clockwise.

You can brush the edges with milk if you wish.

Bake the Galette for 20 minutes, remove it from the oven and crack and an egg in the middle of the gallate. Place the mushroom and onion Galette back in the oven and bake for another 10 minutes.