Preheat the oven to 375°. Line a large rimmed baking sheet with parchment paper. Arrange 12 squares on the sheet and cover with more parchment paper. Top the squares with another baking sheet, bottom side down. If you have another pair of baking sheets, repeat with 12 more squares. Bake the squares for about 35 minutes, until the pastry is golden. Transfer the squares to a rack to cool. Repeat to bake the remaining squares.