Mushroom Puff Pastry Bites

Bahan-bahan (50 porsi)

• 2 tablespoons extra virgin olive oil (divided)
• 1 large yellow onion (thinly sliced)
• 1/2 teaspoon kosher salt
• 16 ounces baby bella mushrooms (sliced)
• 1/2 teaspoon minced garlic
• 2 teaspoons finely chopped fresh thyme leaves (or 1/2 teaspoon dried)
• 1/4 teaspoon ground black pepper
• 1/2 cup shredded Gruyere (Swiss, or similar cheese (about 1 1/2 ounces))
• 2, 10 - inch square sheets frozen puff pastry (thawed)
• 1 egg (beaten)
• 3 tablespoons whole-grain mustard
• Chopped fresh parsley (for garnish)