Grilled Ham and Gouda Sandwich W/Caramelized Onions

This was the "Recipe of the Day" on my Yahoo this morning. It is from www.epicurious.com and sounds FABULOUS!!!

• Ready In: 40 mins
• Serves: 2

Ingredients

• 1  tablespoon extra virgin olive oil
• 1  large onion, thinly sliced
•  unsalted butter, room temperature
• 4  slices  country  white bread or 4  slices  sourdough bread, 1/3-inch-thick
• 4  ounces smoked ham, thinly sliced, divided
• 3  ounces gouda cheese, thinly sliced, divided
• 1  cup frisee, torn into bite-size pieces (about 2 large handfuls)

Directions

1. Heat oil in large nonstick skillet over medium heat.
2. Add onion; sauté 5 minutes.
3. Reduce heat to medium-low; cover and cook until onion is very tender and golden, stirring frequently, about 25 minutes longer.
4. Season with salt and pepper.
5. Cool slightly.
6. Butter 2 bread slices.
7. Place bread, buttered side down, on platter.
8. Divide onion, ham, Gouda cheese, and frisée between bread slices.
9. Top each with another bread slice; butter top slices.
10. Heat another large nonstick skillet over medium heat.
11. Add sandwiches and cook until bread is golden brown and cheese melts, pressing occasionally with spatula, about 4 minutes per side.
12. Cut sandwiches in half diagonally and serve immediately.