Winter Panini with Mustard and Onion

1/4 cup thinly sliced onion, sauteed
4 slices sourdough bread
2 teaspoons Dijon mustard
1/2 cup sharp cheddar

Heat panini press over medium heat. Spread 2 slices bread with mustard and top with Dijon, onion, and cheese. Top with bread slice. Grill 2 minutes or until cheese melts.
Adapted from Cooking Light.