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Caramelized Onion Tart with Spinach and Gruyere

Saturday morning cartoons have done a bang-up job brainwashing me.

Listening to what Toucan Sam told me—that cereal was “part of a complete breakfast”—turned me into a cereal-eating monster, using it as my food crutch since I was tall enough to reach the milk in the refrigerator.

I spent hours poring over the cereal wall in the college cafeteria. I frequently came home from Target with boxes of Marshmallow Treasures, Honeycomb, frosted wheat squares, and Chex galore.

For brunch or lunch, a caramelized onion tart with spinach and Gruyere is a showstopper.
Photo: Casey Barber

It may be a great late-night snack, but it’s no way to start my day.

With Megan Gordon’s new cookbook, Whole-Grain Mornings: New Breakfast Recipes to Span the Seasons, I’m hoping to change that once and for all.

Whole-Grain Mornings cookbook, via www.goodfoodstories.com

Whole-Grain Mornings is more than a collection of breakfast recipes. It’s a thoughtful and personal primer on changing your breakfast perspective.

Reading through the recipes, I wanted to start my days sitting at a window-lined banquette of a cozy Craftsman bungalow, sipping coffee and spooning bites of strawberry oat crisp or a warm farro breakfast bowl.

Megan, who also chronicles her kitchen life on A Sweet Spoonful, has a contemplative writing voice that immediately brings you into her world, and that quality comes through in spades throughout the book’s pages.

If you know Megan from the creative granola she makes for her company Marge Granola, you won’t be disappointed.

She generously shares recipes for signature Marge combinations like apricot pistachio and hazelnut cocoa nib granolas, and brings an irresistibly sweet and savory balance of flavor to each dish in the book.

breakfast rice with pears and kumquats
Photo: Casey Barber

Though the book is organized seasonally, it’s difficult not to want to skip between sections and find inspiration for your morning meals.

The fall section’s creamy breakfast rice topped with honey-poached figs and pistachios was a powerfully nostalgic comfort, reminding me of a milky maple-and-rice dish my mom used to whip up in lieu of Cheerios.

With fresh figs nowhere to be found in New Jersey supermarkets in January, pears and kumquats went into the poaching liquid instead.

Megan fully encourages such substitution and experimentation throughout Whole-Grain Mornings, offering a “make it your own” suggestion at the end of many recipes.

For brunch or lunch, a caramelized onion tart with spinach and Gruyere is a showstopper.
Photo: Casey Barber

Similarly, the cornmeal-millet crust of a smoked salmon tart became the base of my own adaptation: a deeply flavorful spinach, Gruyere, and caramelized onion tart.

While it would do splendidly as a brunch dish, the tart made its way (and then disappeared all too quickly from) our lunch table without a peep of complaint.

Toasty, crunchy, and simple to make in bulk, this tart crust will be a staple in my cooking repertoire for years to come.

For brunch or lunch, try a caramelized onion tart with spinach, Gruyere, and a cornmeal-millet crust from the cookbook Whole-Grain Mornings.
Photo: Casey Barber

I’ll be trying it with ham and peas for Easter, peaches and blueberries in the summer, and certainly making the satisfying caramelized onion tart that follows again and again.

A quick browse through Whole-Grain Mornings is all it takes to inspire a new way of thinking about your breakfast routine.

Whether you’re starting with a new buckwheat pancake recipe, trying your hand at homemade yogurt, or topping last night’s rice with a poached egg the next morning, I have no doubt the recipes in this book will make you a little more excited to get up in the morning.

As a certain cartoon mascot would say, they’re magically delicious.

caramelized onion and spinach tart
For brunch or lunch, try a caramelized onion tart with spinach, Gruyere, and a cornmeal-millet crust from the cookbook Whole-Grain Mornings.

Caramelized Onion Tart with Spinach and Gruyere

Yield: 1 9-inch tart
Prep Time: 30 minutes
Cook Time: 1 hour 45 minutes
Total Time: 2 hours 15 minutes

For brunch or lunch, try a caramelized onion tart with spinach, Gruyere, and a cornmeal-millet crust from the cookbook Whole-Grain Mornings.



  • nonstick baking spray, unsalted butter, or organic canola or vegetable oil for greasing the pan
  • 3/4 cup (90 grams) white whole wheat flour or standard whole wheat flour
  • 1/2 cup (65 grams) fine-ground cornmeal
  • 1 teaspoon kosher salt
  • 6 tablespoons (85 grams) chilled unsalted butter, cut into 1/2-inch cubes
  • 3-4 tablespoons ice water
  • 1/4 cup (45 grams) millet


  • 1 tablespoon unsalted butter
  • 1 medium yellow or sweet onion, thinly sliced into strips
  • 1 large garlic clove, thinly sliced
  • 5 ounces baby spinach
  • 3 large eggs
  • 3 ounces (85 grams) plain Greek yogurt (any fat percentage)
  • 2/3 cup whole milk or reduced fat milk
  • 1 teaspoon kosher salt
  • 1/2 teaspoon freshly ground black pepper
  • 1 pinch freshly grated nutmeg
  • 2 ounces (57 grams; 1/2 cup) coarsely grated Gruyere cheese


Make the crust:

  1. Spritz a 9-inch removable-bottomed tart pan with nonstick baking spray, or grease with oil or butter.
  2. Pulse the flour, cornmeal, and salt together in a food processor. (Don’t have a food processor? Use the instructions for making dough by hand in my pie crust tutorial.)
  3. Add the butter and pulse 8-10 times until the texture is pebbly with pea-size chunks of butter throughout. 
  4. With the food processor running, drizzle 3 tablespoons water through the feed tube until the dough just starts to clump together. Add the final tablespoon of water if needed to make a cohesive but slightly crumbly dough.
  5. Turn the dough out into a large bowl and gently mix the millet into the dough with your hands.
  6. Press the dough evenly with your fingers into the prepared tart pan.
  7. Refrigerate for at least an hour.

Make the filing components:

  1. While the crust chills in the refrigerator, caramelize the onions by melting the butter in a heavy-bottomed skillet over low heat. 
  2. Add the onions and toss to coat, then cook, stirring frequently, for about an hour until the onions are deeply browned and soft.
  3. Scrape the onions into a small bowl and set aside.
  4. Add the garlic to the pan and stir to coat with the residual butter and onion scrapings.
  5. Add the spinach in handfuls and cook, stirring frequently, until the spinach is fully wilted and greatly reduced in volume.
  6. Scrape into a small bowl and set aside.
  7. Whisk the eggs, yogurt, milk, salt, pepper, and nutmeg together in a medium bowl.

Assemble and bake:

  1. Preheat the oven to 400 degrees F.
  2. Place the chilled crust on a rimmed baking sheet (to catch any filling overflow).
  3. Cover with a piece of parchment paper and pie weights or dried beans, then bake for about 15 minutes, until the crust is slightly dry and toasty.
  4. Carefully remove the parchment paper and let the crust cool for about 10 minutes.
  5. Spread the caramelized onions in an even layer across the bottom of the crust. 
  6. Sprinkle the Gruyere cheese in an even layer on top of the onions.
  7. Evenly drop the spinach in small handfuls on top of the Gruyere. 
  8. Pour the egg-and-milk mixture into the tart crust.
  9. Bake for about 30 minutes, until the tart is golden brown and the filling is fully set and puffed.
  10. Transfer to a wire rack and cool for 15 minutes before removing the tart ring, slicing, and serving.


The crust can be chilled up to 3 days in advance and pre-baked a day in advance of filling and finishing the tart.

The onion and spinach can also be cooked up to 2 days in advance of assembly and baking.

Refrigerate all elements and bring back to room temperature before assembling and baking with the egg custard.

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  1. I confess I LOVE cereal (so I really need this book) but Kevin makes the best waffles I’ve ever had – his secret is club soda and no eggs.

  2. My favorite breakfast food is a potato, egg, and refried bean taco. It’s far from healthy, but I really only have them when I go home to Texas. I’ll need this book in my repertoire before we move so that I can resist when I have access to them full time. (The best breakfast tacos are made by someone else, in my book!)

  3. My favorite breakfast on most mornings is toast (I LOVE TOAST!) but if it’s the weekend and I am going all out I love scrambled eggs with mushrooms, onions, and cheese next to a big pile of baked beans and (yes) toast. Heaven!

  4. For years and years I was a cold cereal for breakfast eater, every single day. Recently switched it up with Greek yogurt, maple syrup, chia seeds, berries and my own granola. Never looked back.
    However, I can’t resist a muffin for breakfast if it’s offered!

  5. You can’t beat that morning cold pizza lol. Biscuits with honey butter and eggs are always a hit in my home.

  6. Now that it is cold out, oatmeal has become my breakfast of choice, rolled on the weekdays and steel cut on the weekends. This has replaced my standard homemade yogurt/granola/fruit bowl of warmer weather

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