Maille Mustard Recipe: Stuffed Onions with Mushrooms, Spinach & Gruyère

Stuffed Onions with Maille Black Truffle Mustard

As much as I wanted to make many dishes with Maille Black Truffle and Chablis mustard, the contents of the stoneware jar was like precious gold. A waft of truffle enticed my senses to take a small spoon and dip it into the golden mustard for a taste. The truffle flavor was subtle, with a musky nuance of woodsy mushroom, along with a smooth tang of mustard upon the tongue.

This is, by the way, not the stuff that disgusts Chef Anthony Bourdain. This is the sort of bonafide truffle that would make him stuff his nose into the jar like a truffle pig rooting for its intoxicating odor. Once described by a writer as "the muskiness of a rumpled bed after an afternoon of love in the tropics," decadent and divinely sensual truffles inspire gourmands and sensualists to eye-rolling fits of bliss. Such aphrodisiacs of the earth do not disappoint.

Maille Black Truffle and Chablis Mustard

The black box arrived, with elegant gold writing stamped MAILLE, upon my doorstep in the midst of August, when truffles were just a daydream, as summer temperatures were sweltering, and all I could think about making was iced coffee. But black truffle mustard is irresistible. So I brought the pretty mustard jar along to a family get together in Santa Barbara.

Maille Black Truffle & Chablis Mustard for stuffed onions

The black truffle (Tuber melanosporum) is typically found in the Périgord region of southwest France, however, they can also be found in Asia, North America and North Africa. These fancy fungi can be considered aphrodisiacs, making their appearance in gourmet scenarios where fine dining is an art and an experience of pleasure.


The most memorable black truffle dish was at a pop-up dinner several years ago. I sat at the counter, observing the chef prepare my dish, Miles Davis' Blue in Green played in the background, with the clatter of dishware, conversations and glasses bouncing upon each other, as the slow twirl of the chef's long fork coiled ribbons of cream-coated noodles into a spooled nest upon the plate. Then the chef held something in his hand, not parmesan, but a knobby black truffle, and made the thinnest shavings of it upon the angel hair, which landed like snowflakes so delicately upon the mound. The shavings of black truffle almost melted, as translucent as thin cheese.

onions olives mushrooms

Leafing through French recipes, I knew I'd find the pairing for black truffle mustard. When you have a flavor such as black truffle-- which isn't truly a flavor, per se, but an effluvious aroma that fills the palate via olfactory senses with its musk-- one must find something that will showcase its qualities. Potatoes, yes, risotto, yes. All simple and perfect for black truffles and mustard. Grilled cheese sandwiches, of course. Yet, I found a recipe in Monet's Table, a cookbook that shares the impressionist artist Claude Monet's family recipes. I've made these stuffed onions plenty of times since, adding more of a vegetarian spin on it, omitting the roast pork, chicken or calves' liver it suggests. I've changed the recipe many times depending on what I have on hand, as stuffing onions allows variations.

I gathered a bunch of sweet white onions from the farmers' market, as I'd been cooking for almost 22 people during our family reunion; half of our crowd were children, and not all vegetarians. The stuffed onions were a slow yet easy process, as I was ambitious that week: cooking a large copper pot full of sweet potato and carrot soup, roasting heads of cauliflower with garlic and curry spices, chopping up leaves of kale to add to the cauliflower roast, and meanwhile, as burners were all going and cutting boards were a flurry, making quick veggie quesadillas for anyone who was hungry. I could have stayed in the kitchen for a month and never tired of the job of cooking for so many, as it gave me a deep satisfaction.

This recipe would make a great vegetarian Thanksgiving side or any seasonal fall feast. I've given options for vegan and gluten-free variations as noted. This recipe serves four, however, it can be doubled to serve a larger group. Each onion can also be cut in half to satiate a table of diners quite easily.

Stuffed Onions w/Mushrooms, Spinach, Gruyère & Maille Black Truffle Mustard

adapted from Monet's Table cookbook, originally Charlotte Lysés's Stuffed White Onions

Serves 4  |  Ⓥ GF option 


  • 4 large white onions (Vidalia or Sweet Mayan onions are lovely)

  • 1 cup cremini mushrooms, chopped fine

  • 3-4 garlic cloves, minced

  • 2 tablespoons chopped chives

  • 2 tablespoons dried mixed herbs

  • 2 cups spinach, chopped

  • 4 tablespoons Maille Black Truffle & Chablis Mustard

  • 1/2 cup grated Gruyére cheese (vegan cheese, optional)

  • 1 egg, whisked with a fork (omit for vegan option)

  • 1/2 cup breadcrumbs (GF breadcrumbs, optional)

  • 2 tbsp olive oil, or more as desired

  • 2 tbsp butter (vegan butter, optional)

  • sea salt & pepper to taste


Set the oven to 350ºF degrees. Cut 1/2 slices off the tops of the onions. Blanch the onions by placing in boiling water to cover for about 20 minutes. Drain and cool.

Scoop out the center of each onion with a spoon, leaving enough of a wall of the onion's outer skin to hold the stuffing. (The onions will be soft which makes scooping out the centers easier.)

Place the hollowed onions inside a greased casserole dish, nesting them snugly together for stuffing.

Chop up the onion centers and sauté in a pan on medium flame with a little olive oil, garlic and mushrooms for approximately 10-12 minutes, or until aromatic and well sautéed. I prefer the garlic and onions slightly caramelized, and the mushrooms flavorful and soft. Keep in mind, this will be part of the onion stuffing and will bake within the center of the onions.

Turn down the flame to low. Add the spinach to the sauté mixture in the pan and wilt, coating the spinach with the garlic, onion and mushroom. You may add a pat of butter at this point, unless you are creating a dairy-free dish, in that case, vegan butter works nicely. Turn off flame.

Incorporate all ingredients in the pan with a large wooden spoon, adding the dried herbs, chopped chives, and four (or five!) luscious spoonfuls of Maille Black Truffle & Chablis Mustard.

Mix in the egg (omit if vegan) and breadcrumbs (gluten-free if desired). Combine the mixture. Stuff the onions with the mixture, mounding it slightly above the level of the onion tops. Sprinkle the top of each onion with Gruyére cheese (or vegan cheese) and bake for about 30 minutes or until the cheese is slightly browned.

Remove from the oven and serve with a dollop of mustard on top of each onion.