Slice potatoes into uniform ¼-inch thick pieces using a mandolin or sharp knife. Place them in cold water to prevent browning while preparing other ingredients.
1½ pounds russet potatoes About 3 medium
Heat 1 tablespoon oil in a large skillet over medium-high heat. Add ground beef and cook, breaking apart with a spoon, until deeply browned (5-7 minutes). Drain excess fat and set beef aside.
2 tablespoons vegetable oil Divided, 1 pound lean ground beef 85-90% lean recommended
In the same skillet, add remaining tablespoon of oil. Sauté onions until translucent (4-5 minutes), then add garlic and mushrooms. Cook until mushrooms release liquid and begin to brown (5-7 minutes).
1 large onion Finely chopped, 3 cloves garlic Minced, 8 ounces mushrooms Cremini or white button, 2 tablespoons vegetable oil Divided
Sprinkle flour, paprika, thyme, salt, and pepper over the vegetable mixture. Stir constantly for 1-2 minutes to cook out the raw flour taste.
2 tablespoons all-purpose flour, 1 teaspoon paprika, ½ teaspoon dried thyme, 1 teaspoon salt Adjust to taste, ½ teaspoon black pepper
Gradually pour in beef broth while whisking to prevent lumps. Stir in Worcestershire sauce and dijon mustard, then bring mixture to a simmer.
2 cups beef broth Low sodium recommended, 1 tablespoon Worcestershire sauce, 1 teaspoon dijon mustard
Drain and pat dry the potato slices. Return beef to skillet, then gently fold in potato slices, ensuring they're mostly submerged in liquid.
1½ pounds russet potatoes About 3 medium, 1 pound lean ground beef 85-90% lean recommended
Bring to a gentle simmer, reduce heat to low, cover, and cook for 18-20 minutes, or until potatoes are fork-tender but not falling apart. Stir occasionally to prevent sticking.
Remove skillet from heat and allow to cool slightly. In a small bowl, whisk a few spoonfuls of hot liquid from the skillet into the room-temperature sour cream to temper it.
¾ cup sour cream At room temperature
Gently stir the tempered sour cream into the skillet until fully incorporated and sauce becomes creamy. Do not return to boil after adding sour cream.
¾ cup sour cream At room temperature
Taste and adjust seasoning as needed. Serve hot, garnished with fresh chopped parsley.
1 teaspoon salt Adjust to taste, 2 tablespoons fresh parsley Chopped, ½ teaspoon black pepper