Preheat oven to 425. Line a large baking sheet with parchment paper. Position racks in middle and upper third of oven. On lightly floured surface, roll out puff pastry to a 9 1/2 x 17 1/2 inch rectangle. Using a straight edge, trim pastry to a 9 x 17 inch rectangle. Transfer pastry to baking sheet and poke all over with a fork. Top with another sheet of parchment and another baking sheet land bake for 25 minutes on middle rack, until golden. Remove top baking sheet and parchment paper and bake pastry until lightly browned and dry, about 10 minutes longer. Slide paper and pastry onto a rack and let cool. Meanwhile, in large bowl, toss tomatoes with olive oil and 2 t. thyme and season with salt and pepper. Put the tomatoes on a baking sheet, cut side up and bake on upper rack for about 15 minutes until softened slightly. Let cool. In food processor, puree ricotta cheese until very creamy. Spread the ricotta over cooled pastry and season with salt and pepper. Arrange tomatoes cut side up on the ricotta in 5 rows of 12. Sprinkle lightly with thyme leaves. Using a long knife, cut pastry between tomatoes into 60 squares. Transfer tartlets to platters and serve at once. To make ahead, you can prepared up until pureeing the ricotta. Keep at room temperature for up to 8 hours.
Food and Wine
Makes 5 dozen pieces