02To make the pastry, cut pastry into six four-inch squares, and lightly score a border about 1/4 inch from the edge. Lightly score a criss-cross pattern in the inside of the square. Place on a baking sheet and bake until puffed and lightly browned, 10 to 20 minutes. Remove from oven and poke the center with a fork to allow steam to escape. Cool for 10 minutes.03To make the topping, place a medium sauté pan over medium heat. Melt butter, add leeks and thyme, and sauté until leeks are soft and lightly caramelized, 10 to 15 minutes. Season with salt and pepper to taste; set aside.04Brush the edge of the puff pastry with beaten egg yolk. Spread scored area of pastry with the ricotta base, and sprinkle evenly with Gruyére. Top with leeks and olives. Bake until the edges are golden brown, and the cheese is bubbling, 10 to 14 minutes. Serve hot.