Pub-Style Shepherd's Pie

Ingredients

• 2 Tbsp unsalted butter
• 1 large onion, chopped fine
• 2 medium carrots, peeled and chopped fine
• 4 oz white mushrooms, chopped fine
• 1 1/2 pounds ground sirloin (90/10)
• table salt
• ground black pepper
• 1 Tbsp tomato paste
• 5 Tbsp unbleached all-purpose flour
• 1/4 cup heavy cream
• 1 1/2 cut low-sodium chicken broth
• 1 cup dry, dark stout (like Guinness)
• 2 Tbsp soy sauce
• 2 tsp minced fresh thyme leaves
• 1 cup frozen peas
• 2.5 pounds russet potatoes, peeled and cut into 2-inch pieces
• 2 Tbsp unsalted butter, melted
• 1/3 cup heavy cream, warmed
• 1 large egg, beaten