Shepherds Pie 2

Name: Shepherd's Pie 2
Ingredients: Extra-virgin olive oil, as needed; 2 pounds boneless lamb shoulder or leg, cut into 1/2-inch dice; Kosher salt; 1/2 cup all-purpose flour; 3 carrots, peeled and cut into 1/4-inch dice; 3 ribs celery, cut into 1/4-inch dice; 2 large leeks, white part only, cut into 1/2-inch dice; 2 cloves garlic, smashed and finely chopped; 1/4 cup tomato paste; 1 cup stout beer, such as Guinness; 3 to 4 cups chicken stock; 2 bay leaves; 1 bundle fresh thyme; 2 pounds Yukon gold potatoes, cut into 1-inch dice; 3/4 to 1 cup heavy cream; 2 to 3 tablespoons cold butter; 1 cup frozen peas