My husband and I had this dish in Rome and it was the best lasagna we've ever had. It really tastes like French Onion Soup. I was determined to create it at home! I added the breadcrumbs for some crunch at the end. —Leith Devine
To make carmelized onions: Slice onions, then add to oil in a large frying pan. Cook on medium heat, adding water to deglaze the pan. Cook down until browned and sticky. Keep stirring the onions to prevent burning. Add salt, pepper and and pinch of thyme to taste. This is not a speedy process, but so worth it ! Set aside when completed.
Cheater onions: Cook onions as above, but add 1-2 tsps of gravy browning sauce to speed up the process!
To make bechamel sauce: Melt the butter, then add the flour to make a roux. Whisk constantly on low heat to cook the flour but not brown the roux. Turn the heat up to medium and add the milk in a thin stream, whisking constantly to prevent lumps. Cook the sauce until thickened, approximately 10 minutes. Add 1 cup grated Gruyere cheese and salt and white pepper to taste. If you see lumps, strain the white sauce before adding the cheese.
If desired, add crushed garlic clove to bechamel as it cooks. Remove it before adding the gruyere cheese. The crushed clove will add a mild garlic flavor.
Mix the ricotta cheese with one egg and salt and pepper to taste. Set aside.
Begin with a buttered baking dish. Place down a fresh lasagna sheet, then a thin layer of ricotta, then a thin layer of carmelized onions. Then add a thin layer of bechamel and sprinkle lightly with gruyere cheese. Repeat until casserole dish is almost full.
Put a layer of bechamel last. Mix parmesan cheese with bread crumbs and sprinkle on top.
Bake at 400 degrees for approximately 1/2 hour or until browned and bubbly. Let sit for 15 minutes before cutting so lasagna can firm up.