1. Preheat oven to 375º Fahrenheit. Have a rolling pin, a rimmed cookie sheet, and two sheets of parchment about 15" long available.

For the filling

1. Place the dried mushrooms in a small bowl. Cover with boiling water. Let sit for 30 minutes to 1 hour.
2. Heat a large skillet over medium heat. Add butter.
3. When butter has melted and stops foaming, add leeks and onion to the skillet. Sprinkle lightly with salt and pepper.
4. Cook leeks and onion, stirring occasionally, until softened and edges are brown. Add garlic to the skillet and cook one minute, stirring.
5. Pour red wine vinegar over the leek and onion mixture. Cook, scraping up browned bits, until vinegar has almost completely evaporated.
6. Transfer reconstituted mushrooms and the liquid the soaking liquid into the skillet. Stir in red wine. Bring to a boil. Boil until wine is almost completely evaporated. Pour in cream and cook, stirring occasionally, until thickened. Remove from heat.
7. Stir in thyme.Taste and adjust seasoning if necessary.
8. Allow to cool, uncovered, while making the pastry.

For the pastry

1. Partially fill the lower part of a double boiler with water. Bring to a simmer.
2. In the top part of the double boiler, add mozzarella cheese, almond flour, salt, and dried thyme. Stir to combine. Place over the simmering water in the lower part of the double boiler.
3. Being careful not to burn yourself from steam escaping from the bottom part of the double boiler, stir mixture frequently. Heat until mozzarella melts and mixture forms into a dough.
4. Transfer dough to a sheet of parchment and knead a few times to until ingredients are completely combined. Pat dough into a disk and cover with the second piece of parchment.
5. Roll dough into an approximate 12 inch circle.
6. Remove the top piece of parchment. Slide the bottom piece of parchment containing the dough onto the baking sheet.
7. Spread the filling in the center of the dough, leaving about 3 inches on the edges uncovered.

For the topping

1. Spread the gruyere cheese over filling. Sprinkle the thyme over the cheese. Gently fold the uncovered edges of the dough over the edges of the filling, folding as necessary. Pinch the folds together.
2. Place galette in the preheated oven. Bake for 18-22 minutes, or until golden brown.