Mushroom Puff Pastry Bites

Ingredients (12)

• 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