* 1 to 1.5 lbs of very lean ground beef
* 2 tbsp plus 2 tsp water
* salt and pepper
* 1/2 tsp baking soda
* 2 1/2 pounds of russet potatoes, peeled and cut into 1 inch chunks
* 4 tbsp unsalted butter, melted
* 1/2 cup milk
* 1 large egg yolk
* 8 scallions, green parts only, sliced thin
* 2 tsp vegetable oil
* 1 onion chopped
* 4 oz white mushrooms, trimmed and chopped
* 1 tbsp tomato paste
* 2 garlic cloves, minced
* 2 tbsp red wine
* 2 tbsp AP flour
* 1 1/4 cup beef broth
* 2 tsp Worcestershire sauce
* 1 bay leaf
* 2 carrots, peeled and diced
* 2 tsp cornstarch
1. Toss the beef with 2 tbsp water, 1 tsp salt, 1/4 tsp pepper and baking soda in a bowl until thoroughly combined. Set aside for 20 minutes.
2. Place the cubed potatoes into a saucepan. Add water just enough to cover and 1 tbsp salt. Bring to a boil over high heat. Reduce heat to medium-low and simmer until potatoes are soft, approximately 8-10 minutes. Drain the potatoes and return them to the saucepan. Put the potatoes over low heat and cook to ensure all the water is gone., approximately 1 minute. Remove the pan from heat and mash the potatoes well. Stir in the melted butter. Whisk the egg yolk and milk together and then add to the potatoes. Stir in the scallion greens and season with salt and pepper. Cover and set the potatoes aside.
3.Heat the oil in a broiler safe 10 inch skillet over medium heat until shimmering. Add onion, mushrooms, 1/2 tsp salt and 1/4 tsp pepper. Cook, stirring occasionally until vegetables are just starting to soften, approximately 4-6 minutes. Stir in tomato paste and garlic. Cook and stir for about 2 minutes. Add the red wine and cook, scraping up and browned bits until evaporated, about 1 minute. Stir in flour and cook for 1 minute. Add broth, Worcestershire, bay leaf and carrots. Bring to a boil and scrape up any browned bits. Reduce heat to medium low, add beef in 2 inch chunks to broth and bring to a gentle simmer. Cover and cook until the beef is cooked through, approximately 10-12 minutes. Halfway through this cooking time stir and break up the meat chunks with 2 forks, and then recover.
4. Stir the cornstarch and remaining 2 tsp water together in bowl. Stir cornstarch mixture into the skillet and continue to simmer for 30 seconds. Remove the bay leaf and season again with salt and pepper if needed.
5. Adjust the oven rack to 5 inches from the boiler element.
6. Place the mashed potatoes in a large zip top bag and snip off one corner to create a 1 inch opening. Pipe the potatoes in an even layer over the filling making sure to cover the entire surface. Smooth the potatoes with the back of a spoon, then use the tines of a fork to make ridges through the potatoes. Place the skillet under the broiler and broil until the pototes are golden brown and crusty and the filling is bubbly, approximately 10-15 minutes. Let the pie stand and cool for 10 minutes before serving.