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Caramelized Onion Mushroom Apple Gruyere Bites

Caramelized onion mushroom apple Gruyere bites in crisp mini phyllo shells with jammy onions, browned mushrooms, and melted Gruyere. Cook low-and-slow for deep color, then bake just until the cheese melts and the cups turn 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: 140
Ingredients Equipment Method Notes

Ingredients
  

butter
  • 2 tbsp butter for caramelizing the onions
yellow onion
  • 1 large yellow onion thinly sliced
cremini mushrooms
  • 8 oz cremini mushrooms finely chopped
apple
  • 1 small apple finely diced
fresh thyme leaves
  • 1 tsp fresh thyme leaves stir in near the end
balsamic vinegar
  • 1 tbsp balsamic vinegar adds tang to the filling
salt and pepper
  • salt and pepper to taste season the filling
mini phyllo shells
  • 2 box (15 count each) mini phyllo shells 24 used
shredded Gruyere
  • 1 cup shredded Gruyere for topping
fresh thyme for garnish
  • Fresh thyme for garnish sprinkle before serving

Equipment

  • 1 sheet pan

Method
 

Caramelize the onion filling
  1. Melt butter in a pan over medium-low heat, then cook the sliced onion 20-25 minutes, stirring often, until deep golden and jammy. The onions should look soft, glossy, and caramel-brown.
  2. Add the chopped cremini mushrooms and diced apple, then cook 6-8 minutes, stirring occasionally, until the mushrooms are browned and their liquid has evaporated. Watch for a dry, concentrated filling texture.
  3. Stir in fresh thyme leaves and balsamic vinegar, then season with salt and pepper to taste. The mixture should smell fragrant and taste balanced.
Fill and bake
  1. Preheat the oven to 350F, then arrange the mini phyllo shells on a baking sheet. Keep them spaced so they crisp evenly.
  2. Fill each phyllo shell with the onion mixture, then top with shredded Gruyere. Make sure the cheese covers the filling for bubbling melt.
  3. Bake 8-10 minutes at 350F, until the cheese is melted and the shells are crisp. Look for golden, set cups at the edges.
  4. Garnish with fresh thyme and serve warm. The top should look fresh and aromatic against the melted cheese.

Notes

For the jammi onion base, keep the heat at medium-low and stir often so the onions caramelize without burning. Store leftovers refrigerated up to 2 days, then rewarm in a 350F oven until the shells regain crispness; freezing is not recommended because phyllo can soften. If you want a lighter option, use a reduced-fat Gruyere-style cheese for the same baking method.