Baked Flounder with Black Trumpet Mushroom Beurre Blanc Sauce

In Julia Child’s book, My Life in France, she describes a memorable encounter having beurre blanc sauce over fish for the first time at a restaurant in Paris. And in a scene in the movie Julie & Julia , the actress playing Julia Child, Meryl Streep, describes to her visiting sister how white wine and vinegar are reduced and massive quantities of butter are whipped into submission.

In French, beurre blanc, translated literally, means “white butter.” The sauce is butter whipped to a frothy, tangy, heavenly sensation. That’s the best way I can describe it. And when I opened a small Ziploc bag containing dried black trumpet mushrooms and inhaled the intensly earthy, almost truffle-like aroma, I knew they were destined for beurre blanc.

The mushrooms came to us courtesy of Justin Marx, CEO of Marx Foods, a purveyor of fine foods that supplies restaurants and has branched out to supplying us mere mortal home cooks through an online mail-order site. His online store came up in a Google search when I was looking for a local source for tender fiddlehead ferns. I was amazed at the selection of hard-to-find and wild-foraged produce, mushrooms and other items from the Pacific Northwest.

I later wrote and asked if he’d like to send us some samples that we could test, develop recipes for and write about. An affirmative reply came. We would be getting samples of a variety of wild mushrooms from his source in Eugene. A few days later, a small box came and Charles and I eagerly peeled back the packing tape and gingerly pulled out dried samples of black trumpet, maitake, porcini, lobster, and matsutake mushrooms. We’ve never mail-ordered dried mushrooms before and haven’t ordered anything from Marx Foods before either, so we were eager to examine the quality of what was shipped to us. The mushrooms were individually packed in Ziploc bags w ith labels and there was no doubt about the quality of the product. The mushrooms were either almost entirely in whole pieces, as the black trumpets were, or in nice slices. Broken bits were at a minimum. We opened each bag to smell the aroma of the individual mushrooms and could tell that they were fresh, not stale.

In French cooking, black trumpet mushrooms are favored drenched in cream sauces. The aroma and buttery flavor of fresh black trumpets are described as apricot-like. But when dried and reconstituted in hot water, they have an intensely concentrated earthy aroma, almost like truffles or ripe blue cheese. They have a velvety texture and their dark color makes them stand out from white-fleshed fish when used in a sauce. I reconstituted the dried mushrooms by soaking them about 10 minutes in a little water from our instant-hot water dispenser. Not wanting to throw out the soaking liquid, I added it to the sauce to help flavor the beurre blanc.

“This summer mushroom is relatively easy to find and safe to identify. Black Trumpets are found in mixed deciduous woods, mostly under oaks, on the ground. This mushroom does not typically grow on wood. The stalk is an extension of the trumpet-shaped cap. Coloring of the spore surface and stem can range from salmon to pale grey to nearly black with wrinkles or raised veins rather than gills. The cap and interior are usually darker, salmon brown to black, and hollow top to bottom. They usually appear anywhere from June to September.

Black Trumpets can be difficult to see but once you’ve found one there will often be many more.”

The Forager Press, an online field guide for those interested in foraging for mushrooms, black trumpets (trumpets de mort)

If you’ve never made beurre blanc before, the technique is simple; it just requires quite a bit of elbow grease. If you’re making beurre blanc for fish, it’s best to bake the fillet in the oven so that you will not have to deal with frying the fish while making the sauce at the same time.

The basis of a classic beurre blanc sauce are a dry white wine, white wine vinegar and finely chopped shallots that are slowly reduced over a low flame in a non-reactive saucepan to less than half its original volume. While the sauce is reducing, get three sticks of unsalted butter from the refrigerator and slice them into thin pieces. You don’t want to use butter that’s at room temperature because you’ll run the risk of the fatty solids separating instead of going into suspension. Once the sauce is reduced to about a tablespoon and a half of liquid, turn off the heat completely and quickly whisk while you melt one small slice of cold butter at a time into the sauce. The butter will slowly melt but instead of the milk solids separating, you whisk them into a suspension that will slowly turn the sauce into a frothy mixture. It’s quite a bit of work whisking away until one slice of butter is incorporated into the sauce before adding another. Having a helper in the kitchen is handy. Charles had to give me a break from whisking after I had made it through only two sticks of butter.

But the results are worth it. C’est magnifique!

By the time the sauce is finished, the fish will be ready to come out of the oven and you can finally enjoy the fruits of your labor.

Baked flounder with black trumpet mushroom beurre blanc sauce.

Baked Flounder with Black Trumpet Mushroom Beurre Blanc Sauce — Adapted from Mastering the Art of French Cooking by Julia Child, Simone Beck, and Louisette Bertholle

  1. One flounder fillet per person
  2. 2 tablespoons (30 ml.) olive oil
  3. Salt and ground black pepper to taste
  4. 3 sticks (24 tablespoons or 360 ml.) unsalted butter, chilled and sliced into thin pieces
  5. 2 tablespoons (30 ml.) finely chopped shallots
  6. 1/4 cup (60 ml.) dry white wine
  7. 1/4 cup (60 ml.) white wine vinegar
  8. 5 dried black trumpet mushrooms per fish fillet
  9. 1/4 (1.25 ml.) teaspoon salt
  10. 1/8 teaspoon (.625 ml.) ground white pepper
  • Soak dried black trumpet mushrooms in 2-3 tablespoons (30-45 ml.) of very hot water.
  • Preheat oven to 350ºF (177ºC).
  • Coat an oven-safe baking dish with the olive oil.
  • Place flounder fillets in baking dish and lightly salt and pepper to taste.
  • Place in oven and bake for 10-15 minutes until golden and flaky.
  • While fish is baking, combine wine, white wine vinegar, shallots, salt, ground white pepper and the liquid from the soaking mushrooms into a non-reactive saucepan.
  • Bring to a boil and reduce heat to a simmer and reduce liquid until only about a tablespoon and a half remains.
  • Turn off the flame and immediately begin whisking one slice of butter at a time into the sauce until it melts. Do not stop the process once you begin or the butter may go out of suspension and separate. Once all of the butter has been whisked into the sauce, add the rehydrated mushrooms and gently whisk in.
  • By the time you are done whisking the last of the butter into sauce, the fish should be cooked. If the fish still needs cooking time, you can hold the sauce on the top of your stove without any flame underneath. The heat from your oven below the stovetop should be sufficient to keep the butter from solidifying.
  • Carefully remove the flounder fillets from the baking dish with two spatulas (they will be very delicate) and place them onto individual plates. Cover each piece with beurre blanc sauce and divide the mushrooms evenly between all of the servings.

A good side dish to accompany the fish would be boiled new potatoes and sautéed Brussels sprouts.

Because the sauce is so rich, I would recommend a very dry white wine with good acidity to balance this meal. A pinot gris with a strong mineral backbone like Left Coast Cellars Oregon Pinot Gris works nicely.

Stay tuned as Charles and I come up with other recipes for dried porcini, lobster, maitake and matsutake mushrooms from Marx Foods.


— Vic

About the Author

Victor Panichkul is a journalist and writer by training; a cook, wine lover and photographer by passion; and a lover of the outdoors since moving to Oregon more than 6 years ago. He is a native of Bangkok, Thailand.

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