Preheat over to 400 degrees F.
Line a cookie sheet with parchment. Sprinkle 1 tbsp of cornmeal onto the parchment to cover a 9x9 inch square section.
On a lightly floured surface, roll out the puff pastry into a 9x9 inch square.
Transfer the puff pastry to the parchment with the cornmeal. Using a knife, lightly score a 1-inch border round the edge. Using a fork, prick the bottom of the tart in several places.
Using a pastry brush, brush the whisked egg all over the pastry.
Sprinkle the crumbled goat cheese over the tart, making sure to stay within the scored lines of the border.
Evenly place the cut tomatoes on top of the goat cheese.
Sprinkle pepper to taste.
Bake for 15 minutes. At the 15-minute mark, sprinkle the minced sage on the tart and return to the oven.** Bake for another 5 minutes, or until the pastry is golden brown.
Remove from the oven and sprinkle with Maldon sea salt.
Cut into squares and serve warm.