Main Filling:

• 1 tablespoon olive oil
• 1 medium yellow onion (diced)
• 2 cloves garlic (minced)
• 2 medium carrots (peeled and diced)
• 2 celery stalks (diced)
• 1 pound ground beef (or lamb for traditional shepherd’s pie)
• 1 tablespoon tomato paste
• 1 tablespoon Worcestershire sauce
• 1 cup Guinness stout
• 1 cup beef broth
• 1 teaspoon fresh thyme (or ½ teaspoon dried)
• ½ teaspoon salt
• ¼ teaspoon black pepper
• 1 cup frozen peas
• 2 tablespoons all-purpose flour (optional, for thickening)

For the mashed potato topping:

• 2 pounds russet or Yukon gold potatoes (peeled and cubed)
• 4 tablespoons butter
• ½ cup milk
• ¼ cup sour cream
• Salt and pepper to taste