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A single French onion phyllo cup held between two fingers, showing the layers of filling and cheese.

French Onion Phyllo Cups

Sweet caramelized onions and nutty Gruyère cheese fill crispy phyllo shells in this easy, elegant appetizer.
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Prep Time 15 minutes
Cook Time 50 minutes
Total Time 1 hour 5 minutes
Course Appetizer
Cuisine American
Servings 15

Ingredients
  

  • 2 tablespoons unsalted butter 28 g
  • 3 large sweet onions thinly sliced, about 1.5 lbs / 680 g
  • 1 teaspoon beef bouillon paste or concentrate
  • 1 teaspoon Worcestershire sauce
  • 1 teaspoon fresh thyme leaves plus more for garnish
  • Kosher salt and freshly ground black pepper to taste
  • 2 boxes pre-baked mini phyllo shells (30 shells total) 1.9 oz
  • 3/4 cup shredded Gruyère cheese 85 g

Instructions
 

  • In a large skillet or Dutch oven, melt the butter over medium-low heat. Add the sliced onions, cover, and cook for 10 minutes until they soften, stirring occasionally.
  • Uncover the skillet. Stir in the beef bouillon paste, Worcestershire sauce, and thyme leaves. Season lightly with salt and pepper.
  • Increase the heat to medium. Continue to cook, stirring every 5-10 minutes, for 35-40 minutes. The onions will slowly caramelize, becoming deep brown and jammy.
  • Toward the end of the cooking time for the onions, set an oven rack about 6 inches from the heat source and preheat the broiler. Arrange the phyllo shells on a baking sheet.
  • Taste the onion mixture and adjust seasoning if needed. Spoon about a teaspoon of the mixture into each phyllo shell.
  • Top each filled shell with a generous pinch of shredded Gruyère cheese.
  • Place the baking sheet under the broiler. Broil for 2 to 4 minutes, watching constantly. Remove when the cheese is melted, bubbly, and has browned spots.
  • Let the cups cool on the baking sheet for a few minutes before transferring to a platter. Garnish with a few fresh thyme leaves before serving.

Notes

Every broiler is different. Watch the cups very carefully as they can go from golden to burned in seconds.
The caramelized onion filling can be prepared up to 3 days in advance. Store it in an airtight container in the refrigerator and gently reheat before filling the cups.
For a vegetarian option, swap the beef bouillon for a rich vegetable or mushroom broth concentrate.
Sweet onions like Vidalia or Walla Walla have a higher sugar content, which helps them caramelize beautifully.
Keyword easy appetizer, finger food, french onion phyllo cups, holiday appetizer, party food