Caramelized Onion, Mushroom and Spinach Quiche

Ingredients

• Shortcrust Pastry

  • 1 ½ cups (225 g) unbleached all-purpose flour
  • ¼ tsp salt
  • ½ cup (115 g) cold unsalted butter, diced
  • ½ cup (125 ml) plain yogurt
  • ¼ cup (60 ml) ice water

• Filling

  • 2 small red onions, cut into ¼-inch (5 mm) rounds
  • 1 tbsp (15 ml) balsamic vinegar
  • 2 tbsp (30 ml) olive oil
  • 4 oz (115 g) white mushrooms, thinly sliced
  • 6 cups (140 g) baby spinach, coarsely chopped
  • 8 eggs
  • 1 cup (250 ml) 15% cooking cream or 35% cream
  • ½ cup (50 g) Gruyère cheese, grated