Sunny's Beef Wellington Casserole Recipe | Sunny Anderson | Food Network

Ingredients

• 1 sheet frozen puff pastry, thawed
• 1 large egg
• 2 tablespoons unsalted butter
• 2 tablespoons olive oil
• 3 pounds ground chuck (80% beef/20% fat)
• Kosher salt and freshly ground black pepper
• 4 tablespoons unsalted butter
• 1/4 cup olive oil
• 2 pounds baby bella mushrooms, sliced
• 6 cloves garlic, minced or grated on a rasp grater
• 2 bunches fresh thyme, leaves stripped and chopped
• 1 large red onion, finely chopped
• 2 tablespoons all-purpose flour
• 1/4 cup grainy Dijon mustard
• 3 cups beef stock
• 1/2 cup chopped fresh parsley