2 slices bread
2 tablespoon olive oil
2 thin slices fontina
1/4 cup caramelized onions (5-6 large onions, 1 teaspoon salt, 1 teaspoon sugar, butter, oil)
thinly sliced seared flank steak, cut again into strips on the bias
Cut the onions in half lengthwise, then slice into very thin half rings. For every 1 large onion, heat about 1 teaspoon olive oil in a large, heavy-bottom pan over medium heat. Add the same amount of butter, allow to melt, then add the onions. Stir to coat the onions in oil/butter. Add the salt and sugar. Turn down the heat to medium low and continue to cook the onions until they are soft and deep golden brown, 30-40 minutes. I usually make a lot (like 5-6 large onions) once per month and then add them to just about everything.
To make the sandwich: heat your panini press to medium-high. Brush outside of bread with olive oil. On one slice of bread, lay a slice of cheese, pile caramelized onions, season with black pepper, pile sliced seared flank steak. Cover with the second slice of cheese, and cover with second slice of bread. Press together gently. Place sandwich on the panini press and put down the lid. Cook until bread is golden and the cheese has melted. Make sure to let the sandwich sit for a few minutes before cutting and eating, otherwise the whole thing will fall apart when you take a bite.