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French Onion Patty Melt with Caramelized Onions


  • Author: Jennie Graham
  • Total Time: 1 hour 5 minutes
  • Yield: 4 sandwiches 1x

Description

This French Onion Patty Melt elevates the classic diner sandwich with rich caramelized onions, double layers of melty Swiss and Gruyere cheese, and crispy-edged beef patties—all sandwiched between golden toasted bread with a tangy homemade diner sauce.


Ingredients

Scale
  • 2 lbs ground beef 80/20
  • 1214 slices Swiss cheese
  • 1.5 cups Gruyere cheese, shredded
  • 2 large yellow onions, thinly sliced
  • 68 slices thick cut bread
  • 2.5 tbsp kosher salt
  • 2.5 tbsp black pepper
  • 2 tbsp garlic powder
  • 2 tbsp brown sugar
  • 2 tbsp mayonnaise
  • 2 tbsp ketchup
  • 2 tbsp yellow mustard
  • 1 tbsp pickled relish
  • 1.5 tsp hot sauce

Instructions

  1. Form 2.5-3 oz beef balls and refrigerate for 30 minutes. Mix all diner sauce ingredients and refrigerate until ready.
  2. Preheat grill to 350°F. Add cast iron skillet 2 minutes before cooking.
  3. Add beef balls to hot skillet. Cover with parchment paper and smash firmly with spatula. Cook 1-2 minutes, flip, and season cooked side.
  4. Add sliced onions to skillet. Cook 30-45 minutes until dark brown. Add seasonings and brown sugar halfway through.
  5. Layer sandwich: bread with sauce, onions, Gruyere, patty, Swiss, patty, Swiss, onions, Gruyere, bread with sauce.
  6. Cook assembled sandwiches on clean skillet 1-2 minutes per side until golden. Cool briefly and serve with fries and pickles.

Notes

  • Chill beef balls before cooking to maintain shape and prevent overcooking during the smashing process
  • Use parchment paper when smashing to prevent sticking and ensure even pressure distribution
  • Don’t rush the onion caramelization – low and slow cooking develops the best flavor and color
  • Layer cheese strategically to create maximum melting and flavor integration throughout the sandwich
  • Toast assembled sandwiches on medium heat to ensure cheese melts completely before bread burns
  • Prep Time: 20 minutes
  • Cook Time: 45 minutes
  • Category: Sandwich
  • Method: Grilled
  • Cuisine: American Comfort Food

Nutrition

  • Serving Size: 1 sandwich
  • Calories: 850
  • Sugar: 12g
  • Sodium: 1250mg
  • Fat: 52g
  • Saturated Fat: 24g
  • Unsaturated Fat: 26g
  • Trans Fat: 2g
  • Carbohydrates: 48g
  • Fiber: 3g
  • Protein: 45g
  • Cholesterol: 165mg

Keywords: patty melt, french onion sandwich, diner burger, smash burger sandwich, grilled sandwich, beef patty melt