Ingredients for the pastry1 1/4 cups all-purpose flour 8 tablespoons (115 grams) unsalted butter, cut into tiny cubes 1/2 teaspoon kosher salt 1/4 cup full fat Greek yogurt 2 teaspoons freshly squeezed lemon juice 1/4 cup ice cold water
For the filling1 pound mushrooms (chanterelle, cremini, shitake, enoki, oyster, portabello, button, etc.) Kosher salt and freshly ground black pepper 2 tablespoons unsalted butter 4 cloves garlic, finely minced 1 cup gruyère cheese, coarsely shredded 1/2 cup crème fraîche 1 egg, thoroughly whisked 4 tablespoons chopped fresh herbs (rosemary, thyme, sage) 1 small onion, chopped 2 tablespoons sherry vinegar
- Place the flour and the diced butter in the freezer for at least an hour.
- Add the flour, butter, and salt to the bowl of a food processor and pulse until combined. Add the yogurt and the lemon juice and pulse a few times to incorporate.
- Pour the ice water through the tube and pulse until the dough comes together. It will be sticky. Turn out on to plastic wrap and shape into a ball. Wrap thoroughly in the plastic wrap and refrigerate for 1 to 24 hours).
- Place a piece of parchment paper on the counter and sprinkle flour over its surface. Roll out the ball of dough into a 12" circle. Transfer the parchment and dough to a cookie sheet, cover with plastic wrap, and place it in the refrigerator until ready for use.
- Heat a 10" skillet over medium heat for two minutes. Add the butter, mushrooms, and onion. Turn the heat to medium high and saute, turning occasionally until the mushrooms are golden.
- Add the garlic and stir for one minute. Add the sherry vinegar and cook for 2 minutes. Toss in the remaining gruyère and 3 tablespoons of the chopped herbs, stir for another minute. Remove from heat to cool to room temperature.
- Mix the crème fraîche with half of the gruyère, 1/2 teaspoon salt, and a few grinds of black pepper.
- Remove the galette dough from the refrigerator and spread the crème fraîche mixture over the surface leaving a 1" border.
- Spoon the mushrooms onto the top of the crème fraiche mixture.
- Fold the border of the dough around the mushroom filling, pleating the edge to make it fit.
- Brush the dough, top and sides, with the egg mixture. Place the galette in the oven and bake the galette until golden brown, about 40 minutes.
- Sprinkle the remaining herbs over the hot galette. Serve hot or at room temperature.