Caramelized Onion Tart

Caramelized onion tart
This pastry was made with white flour only, so it is lighter in color than the first tart, which was made with half white, half whole-wheat flour.

If you love attractive food photography, you might want to close your eyes, haha.  The photos don’t do it justice, but this Caramelized Onion and Mushroom Tart is delicious.

I made this caramelized onion tart twice recently and I would happily eat it again anytime. I combined these two recipes: Rustic Onion Tart from Simply Kitchen and Onion and Mushroom Tart from The Kitchn. I wanted a tart with onion, mushroom, and ricotta, but I loved the folded crust of the first recipe. It is a bit heavy for the galette-style crust, and I can see why The Kitchn’s recipe uses a tart pan to support the mushrooms and ricotta. But it worked out fine for me, and I hope it works out for you, too!

Spread ricotta cheese mixture on the pastry
Spread the cheese on the pastry

Both times I approximated the ingredients. It’s pretty flexible in terms of the amounts of the fillings. The second tart didn’t have as many onions, but still turned out great.

There are 3 parts to the recipe:

  1. Onion filling
  2. Cheese filling
  3. Pastry (a pâte brisée recipe is at the bottom, or use premade pie crust)

Onion Filling
About a pound of onions, sliced
8-12 oz of mushrooms, sliced
1 clove garlic, minced
2 TB olive oil
1 TB butter
Salt, pepper
1 tsp balsamic vinegar (optional)

Caramelizing the onions takes about 30-40 mins, so don’t heat them too high or too fast. Keep in mind that they will cook for a while. (Simply Recipes has this great tutorial on the process.)

  1. Heat oil and butter in pan, then add onions and sprinkle with salt.
  2. Cook on medium until onions are translucent, up to 10 mins.
  3. Then turn heat down and stir occasionally.
  4. After about 20 mins total in the pan, add mushrooms and garlic.
  5. Finish cooking (onions will be in for 30-40 min total).
  6. Add balsamic during the last 5 mins of cooking. (or stir in afterward if you forget)
  7. Take off the heat and sprinkle some thyme.
  8. Let this mixture cool a bit before putting into the pastry.

(When you add the mushrooms, some moisture will escape and loosen up the onions. Purists may say that this disrupts the caramelization process, but I didn’t want to dirty a separate pan to cook the mushrooms and garlic. I think it turned out fine, although it may not be technically correct. You could cook them separately and add them together at the end.)

Spread the onions and mushrooms on the ricotta filling
Add the cooled filling

Cheese Filling
3-4 TB ricotta cheese
3/4 to 1 cup shredded gruyère (or cheese of your choice), reserve 1/4 c for sprinkling on top
Salt and pepper

Mix together and set aside.

Tart Assembly

  1. Put parchment paper on baking sheet
  2. Roll out pastry dough to about 14 inches across
  3. Spread cheese in middle, leaving about 2 inches at edges
  4. Place onions and mushrooms on top
  5. Fold dough over edges of filling in sections, working your way around the tart
  6. Sprinkle additional cheese on top

Baking Instructions

  1. Bake at 450° for 10 min
  2. Turn down to 350° for 20-25 min until golden brown
  3. Let cool slightly before cutting
The pastry is folded over the filling and cheese is sprinkled
Fold the pastry over and sprinkle with gruyère

Pâte Brisée
1 1/4 c flour (I mix all-purpose and whole wheat)
1/2 c butter (1 stick), cut into cubes
1/2 tsp salt
1/2 tsp sugar
3-5 TB ice water

Cut butter into flour, salt and sugar until mixture resembles course meal. Try to handle it as little as possible. Add water, one TB at a time until mixture will hold together. Do not add too much water. Flatten into disc and refrigerate at least 30 mins before using. Let sit for 5 mins after removing from fridge and roll out.

Caramelized onion and mushroom tart
The pastry is made with part white, part whole-wheat flour