French Onion Patty Melt Recipe - Ultimate Comfort Food Sandwich - Recipes by Clare

Ingredients

• 3 tablespoons butter
• 3 large yellow onions, thinly sliced
• 2 pounds ground beef (80/20 blend)
• 1 tablespoon ketchup
• ½ teaspoon garlic powder
• 1 teaspoon kosher salt
• ½ teaspoon black pepper
• 2 cups Gruyere cheese, freshly shredded
• 12 slices thick Texas toast bread
• 8 teaspoons mayonnaise (for grilling)
• ⅓ cup mayonnaise
• 1 tablespoon fresh lemon juice
• 1 teaspoon black pepper
• 1 tablespoon fresh garlic, minced (about 3 cloves)
• 1 teaspoon fresh parsley, chopped