Yields: 1 (15- by 10-inch tart), 12 pieces
1 sheet frozen puff pastry, thawed
All-purpose flour (for dusting)
½ tablespoon extra-virgin olive oil, plus more for drizzling
¾ cup freshly grated Emmental or Gruyere cheese
freshly ground black pepper
1 whole egg
1 tablespoon water
1 pound ripe heirloom tomatoes, preferably assorted colors (about 4 small), sliced ¼-inch thick
2 tablespoons roughly chopped fresh herbs, such as oregano, thyme and marjoram
zest of one small lemon (zested on a Microplane)
salt flakes, preferably Maldon or Jacobsen sea salt, to taste
2 tablespoons roughly chopped fresh basil leaves
Arrange an oven rack in the upper middle position. Place an inverted sheet tray on the rack. Preheat oven (and sheet tray) to 375 degrees Fahrenheit.
Roll out puff pastry on a sheet of lightly floured parchment paper in the shape of a large rectangle measuring about 15- by 10-inches. Prick pastry with a fork in a few places, leaving a 1-inch border around the edges, then slide parchment paper onto a second inverted sheet tray.
Brush the ½ tablespoon of olive oil on the pastry dough, staying within the 1-inch border and sprinkle over the cheese and some freshly ground black pepper.
Whisk together egg and water to make an egg wash. Brush egg wash on the edges of the pastry (the 1-inch border).
Arrange tomatoes on top of the oiled portion, overlapping a little if necessary.
Season the tomatoes with the 2 tablespoons of fresh herbs and the lemon zest.
Carefully slide parchment off of the sheet tray and onto the hot sheet tray in the oven and bake for 15 minutes. Rotate the inverted sheet tray 180 degrees. Bake for an additional 15 to 20 minutes until the edges of the pastry are golden brown and puffed up.
Let tart cool for 10 minutes before cutting into 12 pieces.
Before serving, sprinkle over a generous bit of salt, top with chopped basil and drizzle over some extra-virgin olive oil.