100 grams (8 tablespoons) chilled butter, cut into cubes
[i]For the Filling[/i]
2 lbs. (940g) heirloom tomatoes
1 T. herbes de provence
Fresh ground pepper
1 large onion, thinly sliced
[i]To make the tart dough:[/i]
Place the flour in a large bowl. Add the salt and cut the cubed butter into the flour with a pastry cutter or two forks, until the butter pieces are no bigger than lentil size.
Add the egg and mix with a fork until just combined. Form the dough into a ball. If it is too dry, add cold water one teaspoon at a time. Wrap in plastic wrap and chill for at least 30 minutes.
[i]To make the filling[/i]
Slice tomatoes, core and remove seeds. Press gently with a piece of paper towel to remove excess juice.
Coat the bottom of a 10 inch round dish with olive oil and arrange the tomatoes in the pan.
Sprinkle with salt, pepper, herbes de provence and drizzle with olive oil.
Bake at 350F for 30 minutes or until soft.
While the tomatoes are cooking, heat a tsp. of olive oil in a large saucepan and cook the onions on medium low heat, stirring occasionally until very soft and caramelized. Season to taste with salt and pepper.
Roll out the tart dough to a 10 inch round.
Drain the cooked tomatoes of any excess liquid. Spread the onions on top of the tomatoes, then sprinkle with grated parmesan. Cover with the tart dough and tuck the edges in. Use a fork to make a few holes in tart dough to release steam. Bake for another 30-35 minutes, or until golden brown.
To unmold, run a knife around the edges, place a serving dish face down on top and flip the tart over. Sprinkle with additional grated parmesan for serving.