- Two puff pastry sheets – thawed and pliable but still cold
- One lb box mushrooms- chopped finely
- Two onions finely diced
- One cup Gruyere cheese shredded
- Dry thyme leaves
- Olive oil
- Brown mushrooms in 1 tbsp olive oil and 1 tsp butter until soft.
- Remove from heat and place in another bowl.
- Brown onions in pan until sheer and soft. Deglaze pan with about 2-3 tbsp balsamic vinegar. Add mushrooms back in along with cheese. Mix thoroughly. Set aside. At this point, this mixture can be refrigerated and used the next day.
- Roll out softened puff pastry. Brush with egg whites. Place about a mounded teaspoon on puff pastry , 5 across, 6 down, leaving pastry edges between each mound. Score into squares.
- Bake in preheated 400 degree oven for 15-20 min.