Kosher salt and freshly cracked black pepper, to taste
1/4cupbutter
1/4cupflour
4cupswhole milk
2cupsgruyere cheese, grated
3yellow onions, sliced
3tablespoonsunsalted butter
2teaspoonsfresh thyme
1teaspoonWorcestershire sauce
1tablespoonbalsamic vinegar
1quartgood beef stock
Kosher salt and freshly cracked black pepper, to taste
Instructions
Preheat oven to 375°F and grease a 10x14 lasagna pan or a 9x13-inch baking dish.
Toss cubed sourdough bread with olive oil and granulated garlic. Spread on a sheet tray, season with salt and pepper, and bake for 16–20 minutes until golden. Set aside.
Cook lasagna noodles in boiling salted water until al dente. Drain and set in cold water.
Caramelize sliced onions in 3 tablespoons butter over medium-low heat until golden brown.
Stir in flour, then add beef stock, thyme, Worcestershire, and balsamic vinegar. Simmer until thickened. Season to taste. Set aside.
For the béchamel: Melt butter in a saucepan, whisk in flour and toast 30 seconds. Add milk gradually, whisking constantly until thick. Stir in gruyere until melted. Season and blend if needed.
To assemble: Spread a little onion filling on the bottom of the pan. Layer noodles, 1/3 of onion filling, 1/3 croutons, drizzle béchamel. Repeat 2 more times.
Top with mozzarella and remaining gruyere cheese.
Bake uncovered for 35–40 minutes, or until cheese is golden. Let rest 10 minutes before slicing.
Notes
This dish combines rich French onion flavor with creamy béchamel and cheesy lasagna layers. Perfect for cozy gatherings or special dinners.