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Caramelized Onion Mushroom Apple Gruyere Bites

Caramelized onion mushroom apple gruyere bites made in crisp mini phyllo shells with jammy onions, browned mushrooms, and diced apple. Baked at 350°F until the Gruyere melts and the cups turn shatter-crisp.
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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 large yellow onion thinly sliced
cremini mushrooms
  • 8 oz cremini mushrooms finely chopped
apple
  • 1 small apple finely diced
thyme
  • 1 tsp fresh thyme leaves
  • 1 fresh thyme for garnish
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
Gruyere
  • 1 cup shredded Gruyere

Equipment

  • 1 sheet pan

Method
 

Caramelize the filling
  1. Melt butter over medium-low heat, watching it foam slightly but not brown. Cook the onion 20-25 minutes, stirring often, until deep golden and jammy.
  2. Add the chopped mushrooms and diced apple, then cook 6-8 minutes until the mushrooms are browned and their liquid evaporates. Stir frequently so bits toast instead of steaming.
  3. Stir in the fresh thyme leaves and balsamic vinegar, then season with salt and pepper. Cook 1 minute more, keeping the mixture fragrant and thick.
Assemble and bake
  1. Preheat the oven to 350°F, then arrange mini phyllo shells on a sheet pan. Leave space between cups so they crisp evenly.
  2. Fill each phyllo shell with the onion mixture, packing gently so it stays level. Top each with shredded Gruyere.
  3. Bake 8-10 minutes at 350°F until the cheese is melted and the shells are crisp. Look for bubbling and light browning on the edges.
  4. Garnish with fresh thyme and serve warm. Finish right before serving so the phyllo stays crisp.

Notes

Pro tip: slice the onion thinly so it caramelizes into a jammy texture without burning, and keep the heat at medium-low for the full 20-25 minutes. Store baked bites refrigerated up to 2 days; reheat in a 325°F oven for 5-7 minutes to re-crisp the shells. Freeze the cooked onion-mushroom filling (not assembled) up to 2 months, then thaw and rewarm before filling shells. For a lighter swap, use half the Gruyere and add extra shredded part-skim mozzarella for melt with less richness.