Croque Monsieur is a French bistro classic. This is a sandwich made with ham and cheese (often Gruyere) that is topped with Béchamel sauce. I have already made a ham and Gruyere frittata, so I thought why not top it with some Béchamel sauce to make a Croque Monsiuer frittata? It may seem unusual to top a frittata with the sauce. But after all, how unusual is it to top a sandwich with the sauce?
A note about my ambiguity regarding the name. A variant of the Croque Monsieur has a fried egg added on top. This is called a Croque Madame. This frittata doesn’t have a fried egg, but given this is a frittata, the ham and cheese are inside of the egg. So maybe it should be called a Croque Madame frittata. I’ll leave the choice up to you.
Croque Monsieur (or Madame?) frittata
1 tablespoon flour
1 tablespoon butter
1/2 cup hot milk
2 tablespoons grated Gruyere cheese
1/2 teaspoon Dijon mustard
dash of white pepper
dash of nutmeg
3/4 cup ham cut into small pieces
1/2 cup grated Gruyere cheese
grated Gruyere cheese to sprinkle on top
I make the Béchamel sauce first because I don’t seem to have quite enough time while the frittata is cooking on the stove. If you’re quicker, you could do it after you start cooking the frittata. But the finished sauce holds fine while the frittata is cooking.
To make Béchamel sauce, put the butter and flour in a small saucepan over fairly low heat. Stir the flour in as the butter melts and continue to cook and stir for 2 minutes. Remove from heat and add the hot milk, whisking everything together. Place back on the stove, raise the heat to get the sauce bubbling, and cook to thicken, continuing to stir with the whisk or a wooden spoon. This will take about a minute or so. Add the cheese, mustard, pepper, and nutmeg. Continue heating and stirring for a minute to get the cheese melted and mixed through.
Put the eggs into a good-sized mixing bowl and beat just to mix them up. Add a bit of oil to the pan and let it get hot. Add a small amount of egg mixture to the pan to set the bottom of the frittata to prevent sticking. Turn the heat down to medium low. Mix the ham and Gruyere cheese into the eggs and pour the mixture into the pan. (It will help to add the ham a few pieces at a time, as the pieces can stick together.) Cook this for about 5 minutes to set the bottom and sides.
Preheat the broiler. When the 5 minutes cooking on the stove are up, spoon the (thick) Béchamel sauce over the top of the frittata. You want to distribute the sauce over the top, but there is no need to spread the spoonfuls of sauce out to make sure the entire top is covered. As the sauce heats under the broiler, it will soften and spread out evenly by itself. Sprinkle on the additional Gruyere. Place the pan under the broiler, about 6 to 7 inches below. Cook until the top just starts to brown. This is about 1–1/2 to 2 minutes for me, but watch closely.
Remove from the broiler, loosen up the sides with a spatula if necessary, and slide the frittata out onto the serving plate.