Cut to remove each onion’s top and bottom (root end). Standing the onion on the flat cut, cut the onion lengthwise into halves. Remove the outer peel. Lay the onion half-cut side down with the root end toward you. Slice the onion halves down the center to make quarters. Remove the core (root side) by making a small V incision into each quarter onion and discard. With the root or opposite end facing toward you, slice along the grain lines into ¼-inch thick slices. Repeat with remaining onions.
Melt the butter in a large stockpot over medium-low heat. Add the sliced onions. Keep an eye on the onions and stir often at the beginning to allow all the slices to contact the bottom of the pot so they start to release their liquid. In about 45 minutes, they should have released a good amount of liquid. At this point, you can turn the heat up slightly to reduce this liquid at a quicker pace. Return the heat to low once most of the watery liquid is gone.
Place the diffuser under the stockpot to further reduce the heat in contact with the bottom of the pot. Reduce heat to low and stir every ten to 15 minutes, watching to keep from scorching. The color will change from white to ecru to amber to deep brown. This will take five to six hours. Keep a careful eye toward the end to prevent scorching, stirring much more often as you reach the end. You will remove from the heat when you have approximately 1 ½ to 2 cups of deeply caramelized onions.
Sprinkle the flour over the melted onions and cook over medium-high heat, stirring, about 2 to 3 minutes. In the center of the square of cheesecloth, add the bay leaves and thyme, bring the sides of the cheesecloth up and over the contents, and tie into a sachet with kitchen twine. Add the beef stock and sachet to the melted onions. Bring to a low simmer. Simmer for about one hour until reduced by about a third. Add black pepper and Sherry vinegar, taste, and adjust the seasoning. Remove from heat.
Preheat the broiler. Cut twelve ½-inch slices from the baguette and place on a baking sheet. Brush each slice lightly with olive oil on each side and arrange on the baking sheet. Place under the broiler and, watching carefully, toast till golden brown. Remove, turn each slice to expose the other side, and place back under the broiler, toasting the other side till golden brown. Remove and set aside. Leave the broiler on.
Return the onion soup to a simmer on the stovetop. Place six individual, flame-proof soup terrines on the sheet pan. Fill each within ½-inch from the top with the warmed soup. Top each resting two croutons on the soup. Place slices of cheese over the croutons, allowing a little to fold over the sides of the soup tureen. Top with grated cheese to fill any exposed areas.
What could be better on a cold winter’s day than a warm bowl of onion soup? A French-style onion soup, gratinéed with croutons, topped with blistered, stringy Compté cheese. It is soul-satisfying, a bowl of comfort and warmth.
With such few ingredients, it is essential to tease out the best of each. The onions should be cooked very low and slow to caramelize their sugars from the inside out. You don’t want to brown them, which would make the soup taste bitter. You want to coax out the onions’ depth and natural sweetness. This is your soup base.
A good, homemade beef broth adds an earthy dimension. The croutons add texture, and the cheese brings salt, fat, and string-like fun.
This is a complete winter bistro meal on its own. Although soups are a bit more challenging to pair with wine, mainly because it is a liquid paired with another liquid, this soup has enough texture and components to pair well with our 2019 Napa Valley Red Wine or 2021 Sonoma Coast Pinot Noir.