Combine liquid egg, 1/4 cup milk (reserve remaining for mashed potatoes), meatloaf seasoning, ground beef, 1 tsp. salt, and 1/2 tsp. pepper in a large mixing bowl.

Place ground beef mixture on a prepared baking sheet and use wet hands to shape into a loaf approximately 9" by 5". This recipe card should cover it by about 1" on all sides. Brush with ketchup and bake until meatloaf reaches a minimum internal temperature of 160 degrees, 50-60 minutes. Rest 5-10 minutes before slicing. While meatloaf cooks, make potatoes.

After meatloaf has baked 20-25 minutes, peel potatoes and cut into 1" dice. Bring a large pot with diced potatoes covered with water and 1 tsp. salt to a boil. Reduce to a simmer and cook until potatoes are tender, 17-20 minutes. Drain in colander, return to pot, and mash with butter and 1/2 cup milk, adding additional milk 1 Tbsp. at a time until desired consistency is reached. Season to taste with salt, cover, and set aside. While potatoes simmer, roast beans.

After meatloaf has cooked 45 minutes, trim ends off green beans. Place green beans on second prepared baking sheet and toss with 1 Tbsp. olive oil and 1/2 tsp. salt. Spread into a single layer and roast until beans are just tender, 12-16 minutes. While beans roast, start gravy.

Mix 2 cups water into cornstarch. Place small pot over high heat and add demi-glace and cornstarch mixture to pot. Bring to a boil and cook until thickened, 3-4 minutes. Demi-glace has plenty of seasoning; no need to add salt.

Cut meatloaf into 1 1/2" thick slices and serve on a plate with mashed potatoes, beans, and gravy.