Place one unfolded sheet of pastry on a work surface so that a longer end is facing you. Lightly brush the right panel on both sides with water, and fold it back. Cover with the left panel and press down to seal. Brush the top of the pastry with water, and roll it up tightly, starting with the short edge. You should have a 3-inch-wide (7,5cm) log. Roll to extend it to 3 ½ inches (9 cm). Repeat with another sheet of pastry. Wrap in plastic wrap and refrigerate.
In a medium bowl, combine the flour, zest, and salt. Add ½ cup (125ml) of the cream and whisk until no lumps remain. Set aside.
In a bowl, beat the egg and yolks together. Set aside.
In a small saucepan, bring the sugar and ⅔ cup (160ml) of water to a boil over high heat. Don't stir and continue to cook until thermometer reads 230°F (110°C).
Meanwhile, in a medium saucepan, heat the remaining cream (1 ¼ cups or 300ml) over medium-high heat until bubbles form around the edges.
Whisk the hot cream into the flour mixture until smooth. Pour in the hot sugar syrup. Whisking constantly, add the egg mixture. Now pour the mixture you got back into the medium saucepan and cook over low heat, whisking slowly, until it coats the back of a spoon and reaches 170°F (75°C), about 5 minutes. Strain the mixture through a sieve, add the vanilla and let cool.
Cut off the uneven ends of the dough logs and discard them. Cut each log into twelve ¼-inch (0,6cm) slices. Refrigerate the slices.
Work with only 1 slice at a time. Flatten each slice with your fingers on a floured surface and fit into a muffin tin. Press the dough against the bottom and up the sides. Prick the shells with a fork and refrigerate for 20 minutes.
Preheat the oven to 400°F (200°C).
Line the tart shells with foil and fill with rice or dried beans. Bake until the edges of the dough are puffed and brown, about 15 minutes. Cool on a wire rack.
Discard the foil and rice. Fill each tart shell ¾ full (2 ½ tablespoons) with the cooled custard. Bake until the custards barely jiggle in the middle, about 12 minutes. If the tops of the custards are not caramelized, you can put them under the broiler for a minute or so.
Cool on a wire rack. Dust with powdered sugar and cinnamon, if desired.