French Onion Chicken Sandwich

By CheeseDiva

Ingredients

• 1/4 cup apple cider vinegar
• 3 tablespoons prepared coarse-ground mustard
• 3 cloves garlic, minced
• 1 lime, juiced
• 1/2 lemon, juiced
• 1/2 cup brown sugar
• 1 1/2 teaspoons salt
• ground black pepper to taste
• nonstick spray
• 4 skinless, boneless chicken breast, pounded to even flatness
• 2 garlic cloves
• 1 large egg yolk
• 2 teaspoons fresh lemon juice
• 1/2 teaspoon Dijon mustard
• 1/4 cup extra-virgin olive oil
• 3 tablespoons vegetable oil
• 1 tablespoon olive oil
• 1 large white onion, thinly sliced
• 4 slices Swiss cheese
• 8 slices of bread (or 4 hamburger buns)
• 2 cups baby spinach (optional)

Details

Servings 4
Preparation time 25mins
Cooking time 25mins
Adapted from layersofhappiness.com

Preparation

Step 1

Directions:
To make the Chicken:

In a large glass bowl, mix the cider vinegar, mustard, garlic, lime juice, lemon juice, brown sugar, salt, and pepper. Whisk in the olive oil. Place chicken in the mixture. Cover, and marinate 8 hours, or overnight.
To make the aioli:

Mince and mash garlic to a paste with a pinch of salt using a large heavy knife. Whisk together yolk, lemon juice, and mustard in a bowl. Combine oils and add to yolk mixture very slowly, whisking constantly, until all oil is incorporated and mixture is emulsified. Whisk in garlic paste and season with salt and pepper. If aioli is too thick, whisk in 1 or 2 drops of water. Chill, covered, until ready to use.
For the sandwiches:

In large skillet, heat oil over medium heat. Add onion and sugar; cook 25 minutes or until onions are deeply caramelized, stirring frequently. This step can be done up to 3 days in advance. Re-warm onions in microwave or in a small pan on grill before proceeding.

Preheat grill for direct grilling over medium-high heat. Spray chicken with nonstick spray. Transfer chicken to hot grill rack; cover and cook 10 minutes or until chicken loses its pink color throughout and internal temperature reaches 160 degrees F, turning once.

Place cheese slices on chicken pieces. Cover and cook 1 to 2 minutes or until cheese is melted and golden brown. Remove from grill and cover with foil.

Build sandwiches using hamburger buns, spinach, chicken, caramelized onions, and aioli. Serve immediately.