Beef Stroganoff Casserole

Prepare the oven and baking dish

1. Preheat the oven to 375°F. Lightly grease a 9x13-inch (3-quart) baking dish with butter or nonstick cooking spray and set it aside. Having the dish ready now makes the later steps flow smoothly.

Cook the noodles

1. Bring a large pot of water to a boil and add the salt. Cook the egg noodles for 2 minutes less than the package directions, so they are tender but still slightly firm in the center. Drain them well in a colander and set aside. They will finish softening in the oven, so slightly underdone is exactly right.

Brown the mushrooms

1. Melt the butter in a large, deep skillet or Dutch oven over medium-high heat. Add the sliced mushrooms in an even layer and leave them undisturbed for 3 minutes so they can brown. Stir and continue cooking for 3 to 4 minutes more, until they are golden and most of their liquid has cooked away. They will release water at first, this is normal and it will evaporate.

Cook the beef and onion

1. Add the ground beef and diced onion to the skillet, breaking the beef into small pieces with a wooden spoon. Cook for 7 to 8 minutes, until the beef is browned with no pink remaining and reaches 160°F, and the onion is soft. Stir in the garlic, salt, pepper and thyme and cook for 30 seconds, until fragrant. Carefully spoon off any excess fat, leaving about 1 tablespoon in the pan.

Make the sauce

1. Sprinkle the flour over the beef mixture and stir for 1 minute so it coats everything evenly. Stir in the tomato paste, then pour in the beef broth, Worcestershire sauce and Dijon mustard, scraping up any browned bits from the bottom of the pan. Let the sauce simmer gently for 3 to 4 minutes, until it thickens and coats the back of a spoon.

Stir in the creamy ingredients

1. Remove the skillet from the heat and let it cool for 1 to 2 minutes. Stir in the cream cheese until mostly melted, then add the sour cream and stir until the sauce is smooth and glossy. Taste and add a small pinch of salt if needed. Adding the sour cream off the heat helps keep the sauce silky rather than grainy.

Assemble the casserole

1. Add the cooked noodles to the skillet and gently fold until every noodle is coated in sauce. Spread the mixture evenly into the prepared baking dish. In a small bowl, toss the panko with the melted butter until evenly moistened. Scatter the Gruyère over the casserole, then sprinkle the buttered panko over the cheese.

Bake until golden

1. Bake uncovered for 20 to 25 minutes, until the sauce is bubbling around the edges and the topping is golden and crisp. The center should look creamy and set rather than runny.

Rest and serve

1. Let the casserole rest for 5 minutes on a heatproof surface. This allows the sauce to settle so each portion holds together when served. Sprinkle with fresh parsley and serve warm.