Portobello Croque Monsieur
Why we love it:
- 3 Portobello Mushrooms (or 4, about 1.5 pound)
- 1 Tablespoon Extra Virgin Olive Oil
- 1 teaspoon Balsamic Vinegar
- 4 Tablespoons Unsalted Butter (plus 2 additional teaspoons of butter)
- 1⁄4 cup Flour (all purpose)
- 11⁄2 cups Whole Milk
- 1 Tablespoon Whole Grain Mustard
- 1⁄2 teaspoon Nutmeg (freshly grated - use only ¼ teaspoon if it’s pre-ground nutmeg)
- 1⁄2 teaspoon Kosher Salt
- 2 cups Gruyere (grated, divided)
- Bread (8 slices white - country style, brioche, thin or thick all work)
- 4 cups Spring Mix Salad Greens
- 4 Tablespoons Salad Dressing (vinaigrette, or oil and vinegar)
1. PREHEAT THE OVEN TO BROIL
Remove the stem from the mushrooms and slice the cap in ½ - not strips, but the other way, so you have 2 thinner rounds. One might have a hole or two in it, but that’s ok.
Heat the oil (and a dot of butter if you like) in a large sauté pan and sauté the caps until they’re browned and mostly soft, about 5 - 6 minutes, flipping once or twice as needed. When they’re all soft, pour in the balsamic vinegar and let it sizzle for about 30 seconds and turn off the heat. Set aside.
Melt butter in a medium saucepan over medium heat until foamy. Add flour all at once, while stirring constantly until mixture is pale and foamy, about 3 minutes. Gradually pour in the milk, whisking the whole time, until the mixture is smooth. Keep cooking, and stirring very often, until the sauce is thick, about 4 - 6 minutes longer. Remove from heat and whisk in mustard and nutmeg. Season with the salt.
Grate the cheese or slice it really thin. Stir ½ of the cheese into the bechamel sauce and whisk until it melts.
If you can assemble the sandwiches next to the stove so you can keep stirring the bechamel, do that. Otherwise, just wait until the sauce is done for this step.
Make 4 sandwiches using the rest of the cheese and the mushroom caps. Layer the mushrooms on the bread evenly. Place on a baking sheet. Wipe out the pan you used to cook the mushrooms with a paper towel. And return it to the stove.
Use the extra teaspoons of butter in the mushroom pan to make typical grilled cheese sandwiches. Sear one side, then flip when it’s browned and do the other side. You can leave these a little bit lighter than you would if just eating a regular grilled cheese. When done, transfer to the baking sheet.
Wash and dry greens as needed. Toss with salad dressing.
Pour the bechamel over the top of each sandwich in the center and use the back of a spoon to smear it to the edge, it can drip a little bit down the sides. Place sandwiches into the broiler and keep an eye on them for about 3 - 5 minutes, perhaps rotating the pan depending on your oven, until the bechamel is bubbly and just a little browned.
Remove and let cool for a minute or so. Slice in half.
Serve mushroom croque monsieur with salad on the side.