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Caramelized Onion Mushroom Apple Gruyere Bites

Caramelized onion mushroom apple gruyere bites with jammy onions and browned mushrooms baked in crisp mini phyllo shells. Each bite is topped with melted Gruyere and finished with fresh thyme for a French-inspired snack.
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Prep Time 15 minutes
Cook Time 40 minutes
Total Time 55 minutes
Servings: 24 servings
Course: Appetizer
Cuisine: French-inspired
Ingredients Equipment Method Notes

Ingredients
  

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

Equipment

  • 1 sheet pan
  • 1 cast iron skillet

Method
 

Caramelize the onions
  1. Melt the butter in a cast iron skillet over medium-low heat, then cook the thinly sliced onion 20-25 minutes, stirring often, until deep golden and jammy.
  2. Continue cooking until the onions look glossy and thickened rather than watery, keeping the heat at medium-low to avoid browning too fast.
Cook the mushroom-apple filling
  1. Add the finely chopped cremini mushrooms and diced apple to the skillet and cook 6-8 minutes until the mushrooms are browned and the liquid evaporates.
  2. Stir in the fresh thyme leaves and balsamic vinegar, then season with salt and pepper to taste.
Assemble and bake
  1. Preheat the oven to 350F and arrange the mini phyllo shells on a sheet pan.
  2. Fill each phyllo shell with the onion mixture and top with shredded Gruyere.
  3. Bake 8-10 minutes at 350F until the cheese is melted and the shells are crisp, with a bubbling melt at the center.
Garnish and serve
  1. Remove from the oven, garnish with fresh thyme, and serve warm while the cheese is still molten.

Notes

Pro tip: Keep the onions on medium-low and stir often so they turn jammy and sweet without scorching. Store leftovers in the refrigerator up to 3 days; reheat at 325F until warmed and lightly crisp. Freezing: not recommended because phyllo shells soften after thawing. For a lighter option, use a reduced-fat Gruyere or swap in half Gruyere/half part-skim mozzarella for a milder melt.