Veggie-Friendly Mushroom Croque Monsieur Recipe

While a classic croque monsieur recipe is made avec le jambon, not everyone is able or willing to eat pork products, and some prefer to avoid meat altogether. Fortunately, recipe developer Milena Manolova's vegetarian version of the classic sandwich is made "meaty" with mushrooms instead of ham. While you can make it with the plain button kind, she also suggests switching it up with crimini, shiitake, portobello, porcini, or chanterelle mushrooms if you prefer other varieties.

"This mushroom croque monsieur sandwich filled with melted cheese and a silky béchamel sauce is one of my favorite comfort foods," Manolova says. "The Dijon mustard adds a pungent, sharp flavor with a hint of spice," complementing "the buttery and mild flavors of the cheese and béchamel" as well as the "sweet and earthy flavors of the caramelized mushrooms and onions." As for the texture, Manolova notes that the bread gets crunchy in the pan and oven, contrasting nicely with the smooth, creamy, cheesy filling. "Salty and rich," this sandwich can make for a filling lunch all on its own or partner up with soup or salad for an even heartier meal.

Assemble the ingredients for this veggie-friendly mushroom croque monsieur

This sandwich involves several different elements, one of which is a homemade béchamel sauce made from butter, flour, and milk and flavored with salt, nutmeg, and white pepper. "Don't skip the nutmeg when making the béchamel," she says. "It adds a toasty, nutty flavor without being obvious."

To go inside the sandwiches, you'll need mushrooms, an onion, and black pepper, as well as Dijon mustard and two types of cheese: Swiss and parmesan. Oh, and you'll also need bread, of course. The choice is up to you, but Manolova recommends "a sturdy bread that can hold up to the fillings and cooking process without becoming too soggy or falling apart."

Make the béchamel sauce

Before you start on the sandwich prep, you can go ahead and set your oven to 350 F. This will allow it to preheat for the final step.

Now, measure 2 tablespoons of butter and put it into a frying pan to melt over medium heat. Stir in the flour and continue stirring for 30 seconds until you have what resembles a bubbly paste. Manolova's top tip for making the sauce: "Don't let the flour turn brown." Before it can do so, add the milk and stir until your paste is smooth and liquidy. Add ¼ teaspoon of salt plus the nutmeg and white pepper, then cook the sauce for 3-4 minutes, stirring all the while. Once the sauce is thick, take it off the heat.

Sauté the mushrooms and onions

For this next step, you may either use a different pan or wipe out the last one after reserving the béchamel sauce for later. In the pan, melt another tablespoon-sized chunk of butter and cook the onion for a few minutes. Once it's soft and somewhat golden in color, add the mushrooms, black pepper, and remaining salt. Cook the mushrooms for 4-5 minutes, stirring until they are nice and soft. Make sure you cook them until most of the liquid evaporates since, as Manolova explains, "Excess moisture can make the sandwich soggy."

Assemble the sandwiches

Spread 1 side of each slice of bread with mustard and then béchamel. Place 2 slices of cheese onto 2 of the bread slices, then divide the mushroom mixture between them. Top the mushrooms with the rest of the cheese and then close up the sandwiches with the other pieces of bread (condiment-side down, of course).

Cook the sandwiches, bake with more béchamel, and enjoy

Melt the rest of the butter in a pan and fry the sandwiches on both sides until they are golden brown. Once this is done, put them in a parchment-lined baking pan, top them with the rest of the béchamel sauce, and sprinkle them with parmesan. Bake for 5-7 minutes until the cheese is all melted and golden. While different ovens have their own sweet spots, in Manolova's experience, "Placing the tray on the second rack from top to bottom is perfect."

Once the sandwiches are cooked, let them cool down for a few minutes before you chomp into them. As Manolova tells us, "This prevents the fillings from spilling out and allows the cheese to set a bit." While this dish doesn't lend itself very well to leftovers, it's super simple just to cut the recipe in half and make a single sandwich if this is all you need.

Veggie-Friendly Mushroom Croque Monsieur Recipe
4.9 from 24 ratings
Filled with cheese and topped with béchamel, this sandwich has all the gooey comfort of a French croque monsieur, but with earthy mushrooms instead of ham.
Prep Time
Cook Time
grilled cheese sandwich with mushrooms
Total time: 35 minutes
  • 5 tablespoons butter, divided
  • 2 tablespoons flour
  • 1 cup milk
  • ½ teaspoon salt, divided
  • ⅛ teaspoon grated nutmeg
  • ¼ teaspoon white pepper
  • 1 medium yellow onion, sliced
  • 8 ounces sliced white button mushrooms
  • ¼ teaspoon black pepper
  • 2 tablespoons Dijon mustard
  • 4 slices white bread
  • 8 slices Swiss cheese
  • 2 tablespoons grated parmesan cheese
  1. Preheat the oven to 350 F.
  2. To make the béchamel sauce, melt 2 tablespoons butter in a saucepan over medium heat.
  3. Add the flour to the butter and cook it, stirring constantly, for about 30 seconds until a bubbly paste forms.
  4. Pour in the milk and stir the mixture until no flour lumps remain.
  5. Add ¼ teaspoon salt, along with the nutmeg and white pepper, and cook the mixture for 3-4 minutes, stirring until it thickens. Remove from the heat and aside.
  6. In a large pan, melt another tablespoon of butter over medium heat and fry the onion for a few minutes until it turns golden and softens.
  7. Add the mushrooms, black pepper, and remaining salt and cook for 4-5 minutes, stirring frequently, until the mushrooms are soft. Set the mushroom filling aside.
  8. To assemble the sandwiches, spread mustard and béchamel on 1 side of all 4 slices of bread. (You'll use up all of the mustard, but not all of the béchamel sauce.)
  9. Top 2 of the bread slices with 2 slices of cheese each, followed by the mushroom filling and remaining cheese. Close the sandwiches with the other bread slices, with the condiment side facing inward.
  10. Melt the rest of the butter in a pan over medium heat and fry the sandwiches on each side until golden brown.
  11. Put the sandwiches into an oven-safe pan, then spread the rest of the béchamel sauce on top and sprinkle on the parmesan.
  12. Bake the sandwiches for 5-7 minutes until the cheese melts, then allow to cool for 3-5 minutes before serving so the sauce doesn't spill out.
Calories per Serving 210
Total Fat 14.7 g
Saturated Fat 8.5 g
Trans Fat 0.2 g
Cholesterol 39.8 mg
Total Carbohydrates 10.3 g
Dietary Fiber 1.1 g
Total Sugars 2.9 g
Sodium 246.2 mg
Protein 9.9 g
The information shown is Edamam’s estimate based on available ingredients and preparation. It should not be considered a substitute for a professional nutritionist’s advice.
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