French Onion Grilled Cheese

unsalted butter, divided

large yellow onion, halved and thinly sliced

sugar

Kosher salt and freshly ground pepper,

minced fresh thyme leaves

Splash of dry white wine*

baguette slices, cut on an extreme diagonal for maximum surface area

Thinly sliced Gouda cheese (about 2 oz.)

Thinly sliced Gruyere cheese (about 2 oz.)

garlic, peeled

*Feel free to substitute red wine or beef broth if desired