How to Make Onion tart
- in a large sauté pan, cook the onions over medium heat with the olive oil, thyme sprigs, and salt. Cover and cook 40 minutes to an hour until onions are wilted soft. Remove the lid and continue cooking until all moisture is gone and the onions are starting to turn Golden Brown. Pull out the thyme sprigs and discard. Allow to cool while making tart.
- Preheat oven to 400. Cut four Strips, each 1/2 inch wide, from the sheet of puff pastry to form the edges of the tart and set aside.
- On a lightly floured surface, roll the remaining piece of pastry to a thickness of 1/16 inch. Turn the edges to measure the length of each strip. Place on a sheet pan lined with parchment paper. Dock surface with a fork, that is poke lots of small holes to prevent air pockets from forming. Lightly brush with beaten egg. Lay the reserved strips of puff pastry on each edge. Place in the middle of the oven and bake for 10 to 12 minutes until the pastry no longer looks raw and it's just starting to turn Brown.
Spread the onion mixture on the inside of the tart. Brush the edges with egg and return to the oven to continue cooking. Remove when pastry is a Golden Brown, after about 10 minutes. Push olives into the onions to form a grid pattern and sprinkle with fresh thyme leaves. Serves six.