The Best Shepherd's Pie

Ingredients

• 2 tbsp Butter
• 2 lbs Ground Lamb
• 2 lbs Ground Beef
• 2 tbsp Red wine vinegar
• 2 tbsp Worcestershire sauce
• 1 large Onion
• 1/4 cup Beef stock
• 4 cloves Garlic
• 2 tbsp Ketchup
• 3 Carrots
• 1 1/2 cups Frozen peas
• 1 1/2 cups Sweet Corn
• 1 tbsp Fresh Rosemary
• 1 tbsp Fresh Thyme
• 1 tbsp Garlic Powder
• 1 tbsp Onion powder
• 1 tbsp Salt
• 1 tbsp black pepper
• 5 White potatoes
• 3 tbsp Whole Milk
• 3 tbsp sour cream
• 1 Egg Yolk