Preheat the oven to 400 degrees. Unfold the pastry and press the seams together if needed. Slice each side to make strips of about 1 inch wide. Place the big square of pastry on a piece of parchment paper that is on a cookie sheet.
With your finger or a pastry brush, brush about 1 inch of each side of the big center square with the egg wash. Cut and place the strips on the sides and press down gently. Prick the center of the tart with a fork. Brush the whole tart with egg wash and bake at 400 degrees for 25-30 minutes until dark golden brown. **Two times during the baking time pull the tart out and prick the center of the tart with the fork again. Cool.
Using a large non-stick fry pan and vegetable spray and ½ Tablespoon of the butter, fry ½ of the batch of mushrooms until golden. Set aside when the first batch is done and fry the second batch. Do not put too many mushrooms in the pan at once, you want to fry them, not poach them. After the mushrooms are done and removed from the pan, add the last 2 tablespoons of butter, thyme, 2 sprigs of rosemary, and garlic. Cook for 30 seconds. Add flour and stir well. Cook for another 30 seconds. Stir again.
Take the fry pan off the heat and add in the cream and the cooked mushrooms(and juice) into the pan and stir until thickened. If you need to thicken it more, put it back on the heat for just a minute. Take out the rosemary sprigs that have been cooked. Take the mixture off the heat and let it cool for 2 minutes. Add the 3 tablespoons of cream. Stir well.
Place the mushroom mixture in the center of the tart and garnish with the two remaining rosemary sprigs.
There are 4 to 6 servings in this recipe.