Preheat the oven to 450°F. Wash and dry the fresh produce. Halve, peel, and thinly slice the onions. Peel and roughly chop 2 cloves of garlic. Pick the thyme leaves off the stems. Cut the baguette crosswise into equal-sized pieces. Grate the grand cru on the large side of a box grater. Thinly slice the chives. In a small bowl, combine 1 cup of water and chicken concentrate, stir to combine. 

In a medium pot, heat a drizzle of olive oil on medium until hot. Add the sliced onions; season with salt and pepper. Cover and cook, stirring occasionally, 10 to 15 minutes, or until dark and caramelized (if the onions start to burn, add 1 tablespoon of water at a time). Add the chopped garlic and thyme leaves. Cook, stirring occasionally, 2 to 3 minutes, or until softened. Add the vinegar (carefully, as the liquid may splatter) and soy sauce. Cook, stirring constantly, 1 to 2 minutes, or until the liquid has cooked off.

Add the butter. Cook, stirring constantly, 30 seconds to 1 minute, or until melted and combined. Add the flour. Cook, stirring constantly, 1 to 2 minutes, or until thoroughly combined. Carefully Add the stock concentrate mixture and 1 cup of water. Heat to boiling on high. Cook, stirring constantly and scraping up any browned bits (or fond), 2 to 3 minutes, or until slightly thickened and combined. Turn off the heat.

Place two oven-safe bowls on a sheet pan. Evenly divide the soup between the bowls; top each with enough baguette pieces to cover (you may have extra; toast and serve on the side if you’d like). Evenly top with the grated grand cru. Bake 4 to 6 minutes, or until the cheese is melted. If desired, turn your oven to the broil function; broil 2 to 3 minutes, or until the cheese is bubbly and golden brown (watching carefully so it doesn’t burn). Remove from the oven. Let stand at least 2 minutes before serving. Serve the finished soup garnished with the sliced chives. Enjoy!