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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 bubbling melted cheese. French-inspired appetizer with thyme and balsamic for sweet-savory depth.
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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: 95
Ingredients Equipment Method Notes

Ingredients
  

butter
  • 2 tbsp butter
yellow onion
  • 1 yellow onion large, 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 to taste
  • 1 salt and pepper to taste
mini phyllo shells
  • 24 mini phyllo shells use 24 shells (2 boxes of 15-count; keep extras if needed)
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 butter in a skillet over medium-low heat. Cook the onions for 20-25 minutes, stirring often, until deep golden and jammy.
Cook the filling
  1. Add mushrooms and apple to the skillet, then cook for 6-8 minutes. Stir often until the mushrooms are browned and their liquid evaporates.
  2. Stir in fresh thyme leaves and balsamic vinegar, then season with salt and pepper. Cook for 1 minute while the mixture looks glossy and well combined.
Assemble and bake
  1. Preheat the oven to 350F, then arrange the mini phyllo shells on a sheet pan. The shells should sit in a single layer with room for airflow.
  2. Fill each shell with the onion mixture. Add an even mound so each bite is loaded.
  3. Top each filled shell with shredded Gruyere. Bake for 8-10 minutes until the cheese is melted and the shells are crisp.
Finish
  1. Garnish the bites with fresh thyme and serve warm. Finish with a fresh-herb look right after baking.

Notes

Pro tip: keep the onion heat at medium-low and stir often—slow cooking is what turns thin slices deep golden and jammy. Store leftovers in an airtight container in the refrigerator up to 3 days and reheat on a sheet pan at 350F for 5-7 minutes to re-crisp; freezing is not recommended because phyllo softens. For a lighter option, swap half the Gruyere with reduced-fat Gruyere while keeping the same total amount so the cups still melt well.