3 tbsp. vegetable oil, divided
1 medium onion, finely chopped
2 medium carrots, peeled and chopped
2 lb. lean (85 percent) ground beef
Salt and pepper
1 tbsp. tomato paste
4 tbsp. all-purpose flour
1 3/4 cup low-sodium chicken broth
3/4 cup dark beer (stout or porter), or substitute with more broth, if preferred
1 tbsp. Worcestershire
2 tsp. finely chopped fresh thyme, plus several sprigs for garnish if desired
1/2 cup frozen peas
1/2 cup frozen corn
2 lb. russet potatoes, peeled and thinly sliced (3 to 4 medium potatoes)
Preheat oven to 425 degrees.
Heat 1 tablespoon oil in 12-inch cast iron skillet over medium-high heat. Add onion and carrots and cook, stirring, until softened, about 5 to 7 minutes. Add beef, 3/4 teaspoon salt, and 1/2 teaspoon pepper and cook, breaking up meat into small pieces with wooden spoon, until browned, about 8 to 10 minutes. Add tomato paste and cook until paste begins to darken, about 2 minutes. Add the flour and cook, stirring, for another minute.
Reduce the heat to medium. Add broth, beer, Worcestershire sauce and 11/2 teaspoons thyme and simmer, stirring frequently, until mixture is thick but still quite saucy, 8 to 10 minutes. Remove from heat, stir in peas and corn, adjust seasonings, if necessary.
In a large bowl, combine the potatoes, remaining 2 tablespoons oil, remaining 1/2 teaspoon thyme. 3/4 teaspoon salt and 1/4 teaspoon black pepper. Shingle the potatoes over the beef mixture. Transfer to the oven and bake for 30 to 35 minutes, until bubbly around the edges and potatoes are tender and lightly browned. Let stand for 5 minutes. Garnish with thyme sprigs, if desired, and serve.