Heat olive oil in a pan then add onions, balsamic vinegar, salt, and thyme. Sauté until onions are translucent. Add a few tablespoons of water and honey.

Continue to cook onions stirring frequently until the vinegar reduces and the onions are golden brown.

Layer bread with cheese and caramelized onions sandwiching onions between the cheese. The cheese is the glue to the sandwich so make sure it's flush against the bread on each side.

In a heated skillet, melt a pat of butter. Add sandwich to butter, cover, and grill each side on low heat until the cheese is partially melted and the bread is golden brown.