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French Onion Smash Burger Tacos

French onion smash burger tacos with thin, crispy patties, deeply caramelized onions, and melted Swiss or Gruyère in warm flour tortillas. This French-Mexican fusion combines a fast smash-griddle burger method with slow golden onions for a sweet-savory topping.
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Prep Time 20 minutes
Cook Time 35 minutes
Total Time 55 minutes
Servings: 4 servings
Course: Main
Cuisine: French-Mexican Fusion
Calories: 650
Ingredients Equipment Method Notes

Ingredients
  

ground beef
  • 1.5 lb ground beef
salt and pepper to taste
  • 1 salt and pepper to taste
yellow onions
  • 3 yellow onions sliced thin
butter
  • 3 tbsp butter
balsamic vinegar
  • 2 tbsp balsamic vinegar
honey
  • 1 tbsp honey
thyme
  • 1 tsp thyme
beef broth
  • 1 cup beef broth
flour tortillas
  • 8 flour tortillas small
Swiss or Gruyère cheese
  • 8 slices Swiss or Gruyère cheese
fresh parsley
  • 1 fresh parsley for garnish
horseradish mayo
  • 1 horseradish mayo for serving

Equipment

  • 1 cast iron skillet

Method
 

Caramelize the French onion topping
  1. Melt butter in a large skillet over medium heat. Add sliced yellow onions and cook, stirring occasionally, for 20-25 minutes until deeply caramelized and golden brown.
  2. Stir in balsamic vinegar, honey, thyme, and beef broth. Simmer for 5-10 minutes until slightly reduced, then season with salt and pepper.
Smash burger patties
  1. Form 8 small patties from ground beef and season generously with salt and pepper. Heat a cast iron skillet or griddle over high heat until hot.
  2. Smash each patty flat against the hot surface using a spatula. Cook for 2-3 minutes per side until crispy edges form.
  3. Top each smash burger patty with a slice of Swiss or Gruyère cheese and cover to melt. Cook just until the cheese is fully melted.
Warm tortillas and assemble tacos
  1. Warm the flour tortillas in a dry skillet until pliable. Place one smash burger patty in each tortilla.
  2. Top each taco with caramelized onions, then garnish with fresh parsley. Serve with horseradish mayo.

Notes

Pro tip: caramelize the onions until truly golden and jammy—stir occasionally and keep the heat at medium so they brown without burning. Refrigerate leftover caramelized onions in a covered container for up to 4 days and rewarm in a skillet; cooked smash patties reheat best in a hot skillet to re-crisp for 1-2 days (avoid microwave if possible). Freezing: onion mixture freezes up to 2 months; burger patties are not ideal for freezing. Dietary swap: use plant-based ground beef and vegan cheese slices for a dairy-free option with a similar melt.