Makes 12 toasts; serves 4

Instructions:

1. Melt the 2 tbsp. unsoftened butter in a medium skillet over medium heat and sauté the onion until fragrant, 5–7 minutes. Stir in the sugar and chopped thyme.
2. When the onion begins to brown, about 10 additional minutes, add the balsamic vinegar and stock. Cook, stirring occasionally, until the onions are caramelized and most of the liquid has evaporated, 15–20 minutes. If the liquid cooks off completely before the onions are caramelized, add beef broth 1 tbsp. at a time to keep the onions from sticking to the pan.
3. Preheat the oven to 500°F and line a large baking sheet with parchment paper. Slice the baguette into twelve ¾-in.-thick pieces. Slather both sides of each piece with the softened butter. Heat a large skillet over medium-high heat and toast the bread slices, 1–2 minutes per side.
4. Put the toasted bread on the prepared baking sheet. Top each with some of the caramelized onions and cheese. Bake until the cheese is golden brown and melted, about 6 minutes. Top each with thyme leaves and devour!