Mix the flour and salt. Drizzle the olive oil over the flour and cut in with a fork, combining lightly until the mixture resembles coarse meal. Sprinkle water over the flour, a tablespoon at a time, and mix lightly with a fork. With your hands, press the pastry lightly into a ball, wrap in waxed paper, and let rest in the refrigerator at least 20 minutes.
For the rest:.
Chop the shallots and place them in a frying pan with the olive oil. Saute over medium heat until they begin to soften. Lower the heat and add the wine. Slice the white and portobello mushrooms, and add them to the pan, cooking until they soften and release their liquid. Add the spinach, salt, pepper and herbs and cook until the spinach is wilted.
On a wide surface, roll out the dough between two sheets of parchment paper until it becomes a 1/4-inch-thick circle. Arrange the vegetable mixture in the middle of the dough, and loosely gather the dough around the filling, leaving an opening at the top (the dough won't close completely). Place the galette on a new sheet of parchment paper on a baking sheet and bake in the middle of the oven until filling is bubbly and crust is lightly browned, about 35 to 40 minutes.