Vegetable Quiche (based on Chef John's Quiche Lorraine)

Ingredients

• 1 9-inch unbaked pie crust
• 3 oz prociutto, fried until crispy, or 8 slices bacon, cut into 1 inch pieces
• 1/3 cup sliced green onions or 1/2 cup chopped leeks (white and pale green parts only)
• 1/2 cup chopped onion
• 1/2 red bell pepper
• 10 baby portabello mushrooms
• One small bunch baby brocolli
• salt and freshly ground black pepper to taste
• 1 pinch cayenne pepper, or more to taste
• 3 large eggs
• 2 egg yolks
• 1 cup heavy cream
• 3/4 cup milk
• 1 teaspoon chopped fresh thyme
• 6 ounces shredded fontina or gruyere cheese