Grilled onion, cheese, and prosciutto sandwich

Here's another delicious panini for a busy evening. We hit this one with a bit of balsamic vinegar to knock up the taste even more. Saute the onions in a bit of olive oil, then remove the onions and saute the prosciutto in the same pan. Layer the sandwiches as follows and grill them:

Grilled Onion, Gruyere, and Prosciutto Panini

Rye or wheat bread
Sauted onions
Gruyere cheese, grated
Sauted chopped prosciutto
Balsamic vinegar (optional)