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Caramelized Onion Mushroom Apple Gruyere Bites

Caramelized onion mushroom apple Gruyere bites with jammy onions and browned mushrooms nestled in crisp mini phyllo shells. Baked at 350°F until Gruyere melts into bubbly, golden-topped appetizers.
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Prep Time 15 minutes
Cook Time 40 minutes
Total Time 55 minutes
Servings: 24 servings
Course: Appetizer
Cuisine: French-inspired
Calories: 120
Ingredients Equipment Method Notes

Ingredients
  

butter
  • 2 tbsp butter
yellow onion
  • 1 yellow onion thinly sliced
cremini mushrooms
  • 8 oz cremini mushrooms finely chopped
apple
  • 1 apple small, finely diced
fresh thyme leaves
  • 1 tsp fresh thyme leaves
balsamic vinegar
  • 1 tbsp balsamic vinegar
salt and pepper
  • 1 salt and pepper to taste
mini phyllo shells
  • 2 boxes (15 count each) mini phyllo shells 24 used
shredded Gruyere
  • 1 cup shredded Gruyere
fresh thyme for garnish
  • 1 fresh thyme for garnish

Equipment

  • 1 sheet pan

Method
 

Caramelize the onions
  1. Melt the butter over medium-low heat. Cook the sliced yellow onion 20-25 minutes, stirring often, until deep golden and jammy.
Brown and season the filling
  1. Add the chopped cremini mushrooms and diced apple to the pan. Cook 6-8 minutes until the mushrooms are browned and the liquid evaporates.
  2. Stir in the fresh thyme leaves and balsamic vinegar. Season with salt and pepper to taste while the mixture looks glossy and thick.
Assemble and bake
  1. Preheat the oven to 350°F and arrange the mini phyllo shells on a sheet pan. Space them so they stay upright and crisp-looking around the edges.
  2. Fill each shell with the onion mushroom apple mixture and level it lightly. Top each one with shredded Gruyere so it covers the filling.
  3. Bake 8-10 minutes at 350°F until the Gruyere is melted and bubbling and the shells are crisp. Look for golden tops and set cheese before removing.
Finish
  1. Garnish with fresh thyme for garnish right after baking. Serve warm while the cheese is still hot and stretchy.

Notes

Pro tip: keep the onions at a steady medium-low so they turn deep golden without burning; if the pan looks dry, add 1-2 teaspoons water and continue stirring. Store leftovers in an airtight container in the refrigerator for up to 3 days; reheat on a sheet pan at 350°F for 6-8 minutes to re-crisp the phyllo. Freezing is not recommended because phyllo shells lose crunch. For a dairy-light swap, use a reduced-fat Gruyere-style cheese and expect slightly less browning.