Roasted Cauliflower and Caramelized Onion Tart

roasted cauliflower and caramelized onion tart

If you’re anything like me a few years ago, when you see cauliflower, your first reaction is probably along the lines of “pass!” or “ewww.” Whether that is your line of thought or you’re already a cauliflower fanatic, I can’t encourage you enough to give this recipe (or at least roasted cauliflower dusted with cave-aged Gruyère) a chance. If the only preparation of this snowy floret (read: cauliflower…too far?) you have experienced up until this point is the frozen variety in butter or cheese sauce, you’ve seriously been missing out. Seriously.

When roasted with a mere drizzle of olive oil and sprinkle of salt and pepper, it miraculously develops a desirable texture AND flavor, not unlike the more popular potato. However, if you go through the trouble to combine it with a cheesy custard topping, caramelized onions, dijon and a buttery crust, and then, after tasting, you say you still absolutely don’t like cauliflower, I’m going to call your bluff. (While I try not to don’t make it a habit of calling out my dinner guests [or readers], if you can discern, without visual inspection, that it tastes overtly of said cruciferous vegetable extraordinaire, I will be totally shocked.) Basically, it’s a fantastic way to prepare cauliflower for a cauliflower hater, a nice stepping stone.

I love this tart so much that I chose to present this recipe as my final presentation in the cooking course (Basic Foods) I took last year. I like to think that I won a few more cauliflower fans and oh-my-goodness-gluten-free-food-doesn’t-have-to-taste-like-cardboard! believers that day — I’d say so, given that both tarts disappeared and the number of compliments I was given, plus, as additional empirical proof, quite a few people went back for second and third helpings — hopefully, this recipe wins you over too.

golden brown, melted cheese-topped tart

Roasted Cauliflower and Caramelized Onion Tart

(adapted from Smitten Kitchen)

Active Preparation Time: 1 hour+

Inactive Preparation Time: 1 hour+

Baking Time: 40-45 minutes

Serves: 8-12


Savory Tart Shell:

  • 46 grams (1/4 cup plus 2 tablespoons) Millet Flour
  • 46 grams (1/4 cup plus 2 tablespoons) Garbanzo Fava Bean Flour
  • 60 grams (1/4 cup plus 1 tablespoon) Potato Starch
  • 24 grams (3 tablespoons) Arrowroot Starch
  • 1/2 teaspoon Xanthan Gum
  • 1/4 teaspoon Kosher Salt
  • 85 grams (6 tablespoons) cold, Unsalted Butter, diced into 1/2 inch cubes
  • 1 large Egg
  • 1 teaspoon (5 grams) Water
  • Millet Flour, for rolling

Roasted and Caramelized Vegetables:

  • 43 grams (3 tablespoons) Olive Oil, divided
  • 12+ ounces (4 cups, from 1 head) White Cauliflower Florets, no larger than 1″ pieces
  • 1 large Yellow Onion, halved and cut into 1/8″ – 1/4″ slices
  • 1/2 teaspoon Kosher Salt
  • 1/2 teaspoon Ground Black Pepper
  • 1/8 – 1/4 teaspoon Red Pepper Flakes (optional)

Cheese Filling:

  • 2 large Eggs, room temperature
  • 8 ounces Mascarpone Cheese
  • 113 grams (4 ounces or 1/2 cup) Heavy Whipping Cream
  • 113 grams (1 cup) Cave Aged Gruyère, finely shredded
  • 1/8 teaspoon Ground Nutmeg
  • 1/8 teaspoon Ground Black Pepper

For Assembling Tart:

  • 14 grams (1 tablespoon) Dijon Mustard
  • 14 grams (1 tablespoon) Whole Grain Dijon Mustard (optional)
  • 28 grams (1/4 cup) Parmesan Cheese, finely shredded

Optional Side Salad:

  • Mesclun Mix
  • Balsamic Vinegar
  • Olive Oil
  • Kosher Salt and Black Pepper


Make Tart Shell:

Whisk together millet flour through salt in the bowl of a stand mixer, sprinkle in butter pieces. Fit stand mixer with paddle attachment and mix until the butter and flour mixture resembles peas. Add egg and water; mix until the dough just begins to form. If the dough has gotten too warm at this point, form it into a thick disk, wrap tightly with plastic wrap and refrigerate for 15 minutes until firmed up but still pliable enough to roll.

Lightly flour work surface with flour and roll the dough into a 12″ circle. Fit the dough into a 9 1/2″ fluted tart pan with a removable bottom; make sure there aren’t any air bubbles or cracks. Fold the excess dough back into the pan so that the sides of the tart are now about double the thickness of the bottom. Neatly trim away excess dough around the top of the pan.

Freeze for a minimum of 1 hour (up to 3 months, wrap well) before filling and baking.

Prepare vegetables:

While the tart shell chills, roast cauliflower and caramelize onions. Position rack in the center of the oven and preheat to 450°F. In a large bowl, toss cauliflower with 2 tablespoons (28 grams) of the olive oil. Spread in a single layer on a large, rimmed baking sheet lined with parchment paper, sprinkle with salt and pepper; roast for 30-45 minutes or until browned and cooked through, but not mushy, turning half way through. Cool cauliflower to room temperature; break apart into smaller florets about 1/2″ in size. Reduce oven temperature to 350°F.

While cauliflower roasts, heat remaining tablespoon olive oil in a 10″ heavy pan (I use my cast iron skillet) over medium-low heat. Stir in onion and red pepper flakes (if using). Cook onions, stirring occasionally, until lightly caramelized — about 45 minutes total. Cool to room temperature.

Make Cheese Filling:

In a medium bowl, whisk together eggs and Mascarpone until evenly blended. Whisk in heavy cream, nutmeg and pepper. Stir in Gruyère.

Assemble and Bake Tart:

Place the frozen tart shell on a rimmed baking sheet. Spread the bottom of tart crust with mustards. Evenly distribute caramelized onions over the crust; arrange the cauliflower over the onion. Pour cheese mixture over vegetables and sprinkle evenly with Parmesan. Bake until tart is golden and center is set, about 40 minutes.

Transfer the tart to a cooling rack and allow it to cool for about 30 minutes before removing from pan and serving (for a slight semblance of a balanced meal, I recommend serving it with the super simple, tangy, peppery salad below). The tart may be covered and refrigerated for up 3 days (after that quality starts to go downhill), freezing is not recommended.

Make Salad:

For every two cups of mesclun mix, slowly drizzle 1 tablespoon olive oil into 1 tablespoon balsamic vinegar while whisking vigorously. Just before serving with a slice of tart, toss the salad greens with vinaigrette, a pinch of salt and pepper.

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  • Reply
    Christine's Pantry
    September 30, 2011 at 10:05 am

    Congrats on Foodbuzz top 9!

  • Reply
    Becka (The Elegant Eggplant)
    September 30, 2011 at 10:39 am

    This looks absolutely delicious!!!

  • Reply
    heather sage
    October 10, 2011 at 9:15 am

    thank you both!

  • Reply
    October 19, 2011 at 9:45 am

    Yum! I love cauliflower, but the combination of caramelized onions and cauliflower elevate this to tart to perfect….in my opinion. Lovely recipe.

  • Reply
    heather sage
    October 19, 2011 at 10:15 am

    Thank you — I’m so happy to hear from another cauliflower fan! It’s hard not to enjoy all of the flavor and texture combinations packed into one, small slice.

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