Shepherd’s Pie

About 2 lbs potatoes, peeled, quartered
1 tablespoon salt
2 tablespoons butter
1/3 cup milk or half and half
Salt, to taste
Optional: ½ cup shredded cheddar cheese
1 tablespoon butter
1 small onion, diced small
1 large carrot, diced small
1 stalk celery, diced small
1 lb. ground beef 
1 teaspoon Worcestershire sauce 
1 teaspoon thyme
½ teaspoon salt, or to taste
black pepper to taste
1 heaping teaspoon all-purpose flour
1 cup peas (ok if they’re frozen)
1 cup beef broth
1/3 cup chopped fresh parsley 

1. Preheat oven to 400F. 
2. Add the potatoes, salt, and water to cover to a pot. Bring to a boil and cook until tender, about 15 minutes. Drain, add the potatoes back to the pot, and mash using a potato masher. Stir in the butter, milk, cheddar cheese, and salt. If it seems dry, add a little more milk. Mix well and set aside.
3. While potatoes are boiling, heat 1 tablespoon butter in a 10 inch cast-iron skillet over medium heat. Add onion, celery, and carrots, and sauté until softened, about 5 minutes. Pour veggies into a bowl and set aside. Add the ground beef and stir with a spatula, breaking it up into crumbles; cook about 5-7 minutes until no longer pink. 
4. Add the veggies back in along with the Worcestershire sauce, thyme, salt, and pepper and stir together until well combined. Sprinkle over the flour and stir well until completely mixed in. Add the peas and beef broth. Stir and bring to a simmer; cook about 5 minutes until thickened. Turn off heat and stir in parsley.
5. Add small dollops of the mashed potatoes over the top and spread it out evenly using a rubber spatula or fork.
6. Bake about 25-30 minutes until the top turns golden brown. Let cool for 5 minutes before serving.