Vegetarian Croque-Monsieur

Vegetarian Croque-Monsieur

Croque-monsieur is a grilled sandwich you can see very often in France, it’s actually pretty similar as the quiche in the way that it’s fast and easy to make and eat. Which means perfect for a lunch on the go or a dinner after a long day running around. The traditional croque-monsieur comes with ham but since I’m a vegetarian and I love mushrooms, I decided to go for a mushroom grilled sandwich.

The sandwich is usually grilled in a croque-monsieur iron maker – yes, there is an appliance dedicated to it! – but since I don’t have any here, I simply bake it in the oven.

This recipe is a great opportunity to see how to make one of the basics of french cooking, the bechamel sauce. It’s a thick sauce made of butter, flour and milk, seasoned with salt, pepper and nutmeg.

Vegetarian croque-monsieur

Vegetarian croque-monsieur

Grilled mushroom sandwich with a bechamel sauce, and grated gouda.
Recipe for 3 sandwiches.
Prep Time 20 minutes
Cook Time 30 minutes
Total Time 50 minutes
Course Main Course
Cuisine French
Servings 3 people


  • 6 slices sandwich bread
  • 1 cup grated Gouda cheese
  • chopped chives

Bechamel sauce

  • 1 cup milk 250 ml
  • 2 tbsp butter 25 g
  • ¼ cup flour 25 g
  • ½ tsp salt 2.5 g
  • ¼ tsp pepper
  • ¼ tsp nutmeg


  • cup onion
  • 2 cups mushrooms 250 g
  • 1 tsp garlic crushed
  • 1 tbsp white cooking wine
  • 2 tbsp soy sauce
Keyword Bechamel sauce, Gouda cheese, Grilled sandwich, Mushrooms

Bechamel Sauce

Melt the butter in a pot on medium heat, once it starts to sizzle, add the flour and mix with a whisk. Pour about half of the milk and keep stirring until it all comes together. Add the rest of the milk in two times and boil the sauce for a couple of minutes until thickened. Season with salt, pepper and nutmeg. Leave the pot on the side of the stove and stir it from time to time.

Bechamel sauce in a pot with a whisk


Roughly chop the onion and fry in a pan with some olive oil. In the meantime, peel and slice the mushrooms.

Sliced mushrooms on a wooden board

When the onion turns translucent, add a splash of white wine and wait until complete absorption before adding the mushrooms. Cook until all the liquid of the mushrooms is evaporated. Add the garlic and the soy sauce, mix and turn off the stove.

Sliced fried onion, mushrooms and garlic with soy sauce in a frying pan

Assembling Croque-Monsieur

Preheat the oven at 350 °F.

Spread some bechamel sauce on a slice of bread and sprinkle some grated gouda cheese on top.

Slice of bread with bechamel sauce spread on top and grated gouda.

Put the mushroom/onion mix on top.

Mushroom grilled sandwich prep : slice of bread with bechamel sauce spread, grated gouda and fried mushrooms

Spread some bechamel sauce on the second slice of bread and flip it over the first slice to stick them together. Spread some bechamel sauce on the top and sprinkle with gouda cheese.

Mushroom grilled sandwich before baking

Bake for 15 minutes at 350 °F and switch to broil for a couple of minutes. Sprinkle some fresh chives and enjoy the mushroom grilled sandwich with a green salad.

Mushroom grilled sandwich on a plate on top of a green salad.

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