Ham, Cheddar, and Grilled Onion Panini | America's Test Kitchen

Ingredients

• 1/2 cup coarse-grain mustard
• 2 tablespoons prepared horseradish , drained
• 2 teaspoons honey
• 1/4 teaspoon cayenne pepper
• 1 large red onion , halved and sliced 1/2 inch thick
• 1 tablespoon extra virgin olive oil
• 8 slices thick-cut crusty bread
• 1/4 teaspoon table salt
• 1/4 teaspoon black pepper
• 3/4 pound sharp cheddar cheese , thinly sliced, from deli
• 1 pound deli ham , thinly sliced