Gruyere, a firm cow’s-milk cheese from Switzerland, is the standard for onion soup because of its distinctive nutty notes. But I found that a mixture of cheeses provided more complexity and interest. Plus, when Gruyere browns, it can leave a bitter aftertaste. After experimenting, I settled on semi-soft fontal, a melty and much less expensive Italian cheese, which added the creamy note I sought. I also tried, and rejected, combinations with raclette and fontina.
Along with the addition of caramelized onions, mixing cheeses made the difference in my version of croque monsieur. In addition to the fontal/Gruyere mix, I included a layer of Camembert. Remember, it’s all about layering the flavors — even for a grilled ham-and-cheese sandwich.
To build the sandwich, use soft butter on the outsides of bread slices and Dijon mustard on the insides for a nice acid note. I buy a country boule from a bakery. It has substance, and you can control the slice thickness. The airy crumb allows heat to get into the middle of the sandwich; you don’t want a hot sandwich with a cold center. Toast the sandwich over medium heat in a saute pan on both sides. If you rush it, it will toast before it cooks in the middle. For browning the cheese topping, use the upper third of the oven to broil (for a top-heating element).
Deli hams contain a lot of water. To ensure the sandwich would not be soggy, I microwaved the ham portions briefly between paper towels and blotted them before adding them.
While I was putting all this together, I eyed the sliced ham, Mornay sauce and caramelized onions sitting on the counter and had a light-bulb moment. Using scraps left over from making two pies that day, I rolled out a third crust and blind-baked it in a nine-inch tart pan.
It didn’t matter that the reworked pastry was a little tough. I wasn’t making a delicate dish. I covered the baked shell with the onions, topped them with ham and Mornay sauce and broiled what became a gooey, onion-soup-meets-croque-monsieur tart. A small slice makes a perfect winter first course; a larger one with a simple green salad is entree-worthy.
Could I make a meal of an onion by stuffing it? I could combine leftover caramelized onions with chard (more assertive than, say, spinach), hot Italian sausage for protein and heat, mushrooms for earthiness and volume, cream and Parmesan cheese for richness and panko as a binder. If you want the dish to be vegetarian, substitute a hearty grain such as farro for the sausage.
Onions must be scooped out and cooked through before stuffing, otherwise they will remain crunchy. As I scooped out large white ones to bake prior to stuffing, each yielded a cup of onion chunks. It didn’t make sense to use eight additional onions for caramelizing and waste the byproduct from what was to be stuffed, so I chopped the chunks into uniform pieces and caramelized them instead.
In an attempt to combine two steps, I roasted the hollowed-out onions on a layer of the chopped onions drizzled with oil, hoping that the latter would caramelize during the 40-minute cooking time. They cooked unevenly — some burned — and went into the trash.
For a second go, I placed the hollowed-out onions on a bed of the chopped onions and oven-steamed them in a foil-covered pan that really added nothing to the final result — except more work. Writing this, it occurs to me that reducing heavy cream into an easy sauce flavored with those onions, a fresh bay leaf, garlic, salt, pepper, thyme and rosemary (or the oregano that helped flavor the stuffing) would have added an elegant finishing touch to the dish.
Over the next few days, the caramelized onions from my various test batches got mixed with sour cream for a quick dip and heated with cream, chopped spinach and garlic for a side dish. I have no doubt that in the coming cold days and nights, with the aid of quarts of oniony broth in my freezer, I will be fulfilling the promise of a satisfying French onion soup.
Hagedorn’s column appears monthly in Food.