Step 1

Heat a large Dutch oven over medium-high heat. Add the butter and onions and stir until the butter is melted. Add the salt and sugar, then cover the Dutch oven with a lid. Cook, stirring occasionally, until the onions are translucent and liquids have been released, about 20 minutes. Uncover, reduce the heat to medium and continue to cook until the onions are uniformly caramelized, 40 to 45 minutes. (Be sure to deglaze with about 1/4 cup water and scrape with a wooden spoon when the onions get very dark and start sticking to the bottom of the pan; do this at least TWICE.)

Step 2

Preheat the oven to 400 degrees F.

Step 3

Deglaze the pan with the sherry while scraping the fond off the bottom of the pan. Let simmer for 2 minutes, then add the broth, thyme and bay leaf. Bring to a light simmer, uncovered, for about 30 minutes. Remove the thyme sprigs and bay leaves. Season to taste with salt and pepper.

Step 4

Meanwhile, brush the baguettes with olive oil and place on a sheet pan. Bake until golden and crispy, about 7 minutes. Let cool.

Step 5

Preheat the oven to high broil.

Step 6

Spoon the soup, scooping from the bottom first, to ensure you get ample amounts of that wonderful onion, into ovenproof crocks or bowls. Fill to the brim and top with 2 croutons and 2 slices Gruyère. Broil until golden and bubbly, 2 to 4 minutes. Serve!