Mushroom Crust Cheese Quiche

Ingredients

• 1 1/2 cups all-purpose flour
• 1/2 cup butter, cold and cubed
• 1/4 cup ice-cold water
• 1 tablespoon olive oil
• 1 onion, finely chopped
• 2 cups mushrooms, sliced
• 4 eggs
• 1 cup milk
• 1/2 cup heavy cream
• 1 cup shredded Gruyere cheese
• Salt and pepper to taste
• Fresh parsley, chopped (for garnish)