Grammys Shepherds Pie

Name: Grammy's Shepherd's Pie
Ingredients: 3 large russet potatoes (about 2 pounds), peeled and coarsely diced; Kosher salt; 3/4 cup sour cream; 1 large egg; Freshly ground black pepper; 1/2 bunch scallions, green parts only, sliced; 4 tablespoons unsalted butter; 2 carrots, finely diced; 2 ribs celery, finely diced; 1 onion, finely diced; 1 pound ground beef substitute (such as soy crumbles); 2 tablespoons all-purpose flour; 1 cup porter beer, at room temperature; 1 cup vegetable stock, warmed; 1/2 cup frozen corn; 1/2 cup frozen shelled edamame; 2 tablespoons vegetarian steak sauce; 1 to 2 teaspoons garlic powder; 1/4 to 1/2 teaspoon red pepper flakes; Kosher salt and freshly ground black pepper