Ingredients:

  • 2 tbsp (28g) Unsalted butter
  • 1 tbsp (15ml) Extra virgin olive oil
  • 2 Large yellow onions (approx. 500g), thinly sliced
  • 1/4 tsp Baking soda
  • 8 oz (225g) Cremini mushrooms, finely chopped
  • 2 cloves Garlic, minced
  • 1 tbsp (15ml) Balsamic vinegar
  • 1 tsp Fresh thyme leaves
  • 1/2 tsp Sea salt
  • 1/4 tsp Cracked black pepper
  • 17.3 oz (490g) Frozen puff pastry, thawed
  • 1.5 cups (150g) Gruyère cheese, freshly shredded
  • 1 large Egg
  • 1 tbsp Water

Instructions:

  1. Thinly slice your 500g of onions. You want them uniform so they cook at the same rate. Finely chop the 225g of mushrooms; the smaller they are, the better they'll nestle into the onion jam.
  2. Melt the 28g of butter and 15ml of olive oil in a large skillet over medium heat. Add the onions and 1/4 tsp baking soda. Sauté for about 15 minutes until they turn a deep, jammy amber.
  3. Push the onions to the edge of the pan and drop in your chopped mushrooms. Increase the heat slightly. Sauté for 8 minutes until the mushroom liquid has completely evaporated.
  4. Stir in the 2 minced garlic cloves, 1 tsp thyme, salt, and pepper. Pour in the 15ml of balsamic vinegar, scraping up any browned bits from the bottom of the pan. Cook for 2 more minutes until the vinegar has reduced to a glaze. Let the mixture cool.
  5. Unfold your 490g of thawed puff pastry onto a lightly floured surface. Cut each sheet into 12 squares (24 total). Place them on a parchment lined baking sheet and score a small border about 1cm from the edge using a knife.
  6. Distribute the 150g of shredded Gruyère evenly among the centers of the pastry squares, staying within your scored border. This acts as a moisture shield for the pastry.
  7. Spoon about a tablespoon of the onion and mushroom mixture over the cheese. Don't overfill, or the pastry won't have room to puff up around the sides.
  8. Whisk the egg and 1 tbsp water. Brush the exposed edges of the pastry. This ensures a deep mahogany finish rather than a pale, floury look.
  9. Bake at 200°C (400°F) for 15 to 20 minutes until the pastry is puffed and the cheese is sizzling. The aroma of toasted butter and thyme should fill your kitchen.