Slow Cooker Salisbury Steak

Bahan-bahan (6 porsi)

• 6 ounces mushrooms (sliced)
• ½ medium yellow onion (sliced)
• 1 ½ cups beef broth (or low sodium beef broth)
• 1 ounce brown gravy mix (1 packet)
• 2 tablespoons ketchup
• 1 teaspoon Dijon mustard
• 2 tablespoons chopped fresh parsley (or 2 teaspoons dried)
• 2 tablespoons cornstarch
• 4 tablespoons water
• 1 ½ pounds lean ground beef
• 1 egg yolk
• ¼ cup minced onion
• ⅓ cup Panko bread crumbs
• 3 tablespoons milk
• 1 clove garlic (minced)
• ¾ teaspoon salt
• ¼ teaspoon black pepper