Vegetable Pot Pie | America's Test Kitchen

Ingredients

• 1 single-crust pie dough
• 4 tablespoons unsalted butter
• 1 onion, chopped fine
• 8 ounces cremini mushrooms, trimmed and quartered if large or halved if small
• Salt and pepper
• 1 sweet potato (12 ounces), peeled and cut into ½-inch pieces
• 8 ounces turnips, peeled and cut into ½-inch pieces
• 3 garlic cloves, minced
• 1/2 teaspoon grated lemon zest plus 1 tablespoon juice
• 8 ounces Swiss chard, stemmed and cut into 1-inch pieces
• 2 tablespoons all-purpose flour
• 2 cups vegetable broth
• 1 ounce Parmesan cheese, grated (½ cup)
• 2 tablespoons minced fresh parsley
• 1 large egg
• 1 teaspoon water