Preheat oven to 425 degrees F.
Heat 2 large saute pans over high heat. Working in batches divide the olive oil between the 2 pans. When the oil is hot but not quite smoking, add the mushrooms, season with gray salt and pepper, add the butter to each pan and allow to caramelize. Once mushrooms have cooked down to half their volume, transfer all mushrooms to 1 pan. Add the shallots and garlic and cook until the light brown and fragrant. Add the thyme until it crackles. Add the cream and bring up to a simmer. Reduce the cream by about half and stir in the grated parmesan, and the lemon juice. Shut off the flame and quickly stir in the beaten egg. Remove from the stove and let cool to room temperature. Add parsley and stir.
While mushroom mixture is cooling, roll out the pastry dough on a floured surface. Roll the dough out so that it will line a 10-inch removable bottom tart pan. Line the dough with parchment paper and fill with the dry beans. Bake for 10 to 12 minutes, remove from the oven and let cool to room temperature. Remove beans and paper.
Lower oven temperature to 400 degrees F.
When both the filling and shell have cooled to room temperature fill the shell with the mushroom mixture and top with the crumbled blue cheese. Arrange the tart mold on a cookie sheet and bake for 20 to 30 minutes. Remove from the oven and allow to cool to room temperature before serving. Slice in wedges and serve.