Make Ahead

Mustard Greens Tart with Caramelized Onions and Gruyere

March  8, 2011
4 Ratings
  • Serves 4
Author Notes

This tart is all about building layers of flavor. It starts with a base of ricotta and greek yogurt; a layer of gruyere cheese; and then a mixture of caramelized onions and sautéed, garlicky mustard greens. This same filling could work in a tart shell or even a galette, but in my mind the flaky, buttery puff pastry makes the perfect canvas. Note: the proportions below are for an 8 oz sheet of puff pastry; I'd recommend doubling the filling if you're using a sheet that's 14 oz. A sheet of Dufour puff pastry is 14 oz, and while pricey, it puffs up sky high and is completely worth the splurge. —EmilyC

What You'll Need
  • 1 sheet (about 8 oz) frozen all-butter puff pastry, slightly thawed
  • 2 egg yolks
  • 4 tablespoons plus 1 teaspoon olive oil
  • 3/4 pound yellow onion, thinly sliced (about 3 cups)
  • 2 teaspoons thyme, finely chopped
  • 1 bunch mustard greens, stems and center ribs discarded, leaves cut into wide ribbons
  • 2 large garlic cloves, minced
  • 1/4 cup whole milk ricotta
  • 2 tablespoons whole milk greek yogurt
  • 1/2 cup gruyere cheese, shredded
  • kosher salt and pepper, to taste
  • 1/2 lemon, for juicing
  1. Heat a large sauté pan over medium-high heat for 1 to 2 minutes. Add 2 T olive oil, then the onions and thyme. Stir to coat the onions in the oil. Once the onions have started to color, lower the heat, stir in a few pinches of salt and pepper, and cook until the onions are a golden, amber color -- about 25 to 30 minutes. Take your time with this step; the flavor is worth it.
  2. Meanwhile, heat a large sauté pan or dutch oven over medium heat for 1 to 2 minutes. Add 2 T olive oil, then the garlic and cook, stirring frequently, about 30 seconds. Add the greens and toss with tongs to coat uniformly with oil. When they begin to wilt, add a few tablespoons of water, cover, and cook for about 5 minutes, stirring occasionally. Uncover and continue to cook until greens are tender and water has evaporated, another 1 to 2 minutes. Season with salt (no pepper is needed because they're naturally peppery!). Remove from pan; wrap the mustard greens in a dish towel (or paper towels) and squeeze to remove excess moisture. Don't skip this step because it will prevent a soggy crust.
  3. Mix together the caramelized onions and mustard greens; set aside.
  4. Preheat the oven to 400 degrees F.
  5. Combine ricotta, egg yolk, yogurt and 1 teaspoon of olive oil in the bowl of a food processor. Puree until smooth, then season with salt and pepper; set aside.
  6. Place the slightly thawed puff-pastry sheet on a parchment-lined baking sheet. Make an egg wash by combining 1 egg yolk with enough water to loosen. Score a 1/4-inch border around the edge of the pastry, then brush the border with the egg wash.
  7. To assemble the tart: Spread the ricotta mixture evenly on the puff pastry within the border. Sprinkle the gruyere over the ricotta. Arrange the caramelized onion - mustard greens mixture on top.
  8. Bake the tart for about 25 minutes. The crust should turn golden brown and the cheese should bubble. Lift up the crust to make sure it's crisp and fully cooked before removing from the oven. (I find it helpful to use a spatula to peek under the tart -- the crust should be pretty crisp and stiff, with slight give in the middle, when it's done.)
  9. Squeeze lemon juice over the tart and serve.

See what other Food52ers are saying.

  • ChristineC
  • thirdchild
  • gingerroot
  • AntoniaJames
  • Midge

Recipe by: EmilyC

I'm a home cook. I love salads. Two things you'll always find in my refrigerator are lemons and butter, and in my pantry good quality chocolate and the makings for chocolate chip cookies.

14 Reviews

ChristineC November 25, 2015
I just did a test run on this recipe. It's a winner! I wanted to use up some kale greens I already had, so I subbed those for mustard greens and it worked great. Question: have you ever used egg whites instead of yolk for the ricotta mixture? This is going to our Thanksgiving gathering! Thank you for sharing the recipe!
EmilyC November 25, 2015
So happy to hear that the tart turned out well for you, and that you're making it for Thanksgiving! I've never used egg whites, but I think they'd work okay, as would a whole egg instead of two yolks. You can always add a bit more ricotta and/or greek yogurt if the mixture seems too loose. Happy Thanksgiving!
thirdchild June 19, 2012
Thanks for the great recipe. We have made it twice now, using mustard greens and chard from the garden. I added a bit of balsamic to the greens, and rather than putting them in a towel to get out the moisture, I just squeezed them on one side of the pan with my wooden spatula. Worked fine.
EmilyC September 6, 2012
So sorry for the last response -- I'm just now seeing your comment! I'm so happy you're enjoying the recipe -- thanks for letting me know!
thirdchild June 19, 2012
I thought I would let you know that we are really enjoying this tart, prepared with mustard greens from our garden. Thanks for the recipe.
gingerroot September 8, 2011
This sounds amazing. My CSA keeps me supplied with a steady course of mustard greens and I can't wait to try this.
EmilyC September 8, 2011
Thanks so much, gingerroot! Let me know if you try it!
AntoniaJames September 1, 2011
This looks so tasty! I've not used mustard greens much. That's going to change this week, when I try this. Yummmmm. ;o)
EmilyC September 2, 2011
Thanks AJ! I'd be thrilled if you try it! The first time I made it, I used puff pastry from Trader Joe's. For a real treat, I've also used Dufour puff pastry, which is a bit pricey but puffs up sky high and tastes wonderful. A sheet of it is 14 oz, so I doubled the ingredients and that worked well. Enjoy!
Midge March 9, 2011
Yum. I'm with you on mustard greens, love their subtle smokiness.
hardlikearmour March 9, 2011
I second TiggyBee's comment! This looks killer.
EmilyC March 9, 2011
Thank you, and many congrats on your fondue recipe -- it looks killer too!
TiggyBee March 9, 2011
I love mustard greens!! Nice!!
EmilyC March 9, 2011
Thanks...I think this tart made my husband a fan of them, too!