Melt the butter in a large stock pot or dutch-oven over medium heat. Once melted, add in the onions and a pinch of kosher salt. Sauté until tender and translucent, about 5-7 minutes. Stir in the garlic and This Little Goat went to Hong Kong sauce until coated. Reduce the heat to medium-low and continue cooking, stirring occasionally, until the onions are deep golden brown and well caramelized, about 20-25 minutes. Whisk in the flour until no large clumps remain and let cook for about 1 minute more.\nStir in the stock and thyme, mixing to combine. Bring the mixture to a broil, then reduce the heat to a gentle simmer. Let simmer, uncovered, for about 20 minutes more, allowing the flavors to meld and the soup to thicken.\nMeanwhile, preheat the oven to 400 degrees. Place baguette on a baking sheet and bake for about 5 minutes, flipping once halfway through, until lightly browned on both sides. Remove from the oven and turn the oven to broil.\nLadle the soup into oven-safe bowls and place on a baking sheet. Top each bowl with a slice or two of toasted baguette and a pile of shredded gruyere. Broil on the upper oven rack for about 2-4 minutes (watching closely to avoid burning), until the cheese is melted and bubbly. Let cool slightly, then serve!