Shepherd's Pie

Name: Shepherd's Pie
Cuisine: European, British
Ingredients: 1.5 lbs ground beef, 93%; salt and pepper; .5 tsp baking soda; 2.5 lbs russet potatoes; 4 tbsp unsalted butter; .5 c milk; 1 egg yolk; 2 tsp vegetable oil; 1 onion; 4 oz white mushrooms; 1 tbsp tomato paste; 2 garlic cloves; 2 tbsp Madeira; 2 tbsp all purpose flour; 1.25 c beef broth; 2 carrots; 2 tsp Worcestershire sauce; 2 sprigs thyme; 1 bay leaf