Peppery spaetzle is the perfect foil for the seared, savory beef and rich sauce. When all the elements of this dish come together they create something truly special.
For the spaetzle:1.
Season a large pot of water with salt and bring to a boil. Fill a large bowl with ice and water.2.
Combine the flour with 1 teaspoon pepper and a large pinch of salt in a bowl. Lightly beat the eggs and milk together in a separate bowl and then stir into the flour. If necessary, add a little more milk to make a batter about the consistency of pancake batter.3.
Scoop up 1 heaping tablespoon of the batter and drop it into the boiling water; small pieces may break off, but the bulk should remain largely intact and form a rough disk. Continue to scoop and drop the batter into the pot, using about one-fourth of the batter for each batch and stirring to make sure none of the dumplings stick to the bottom of the pot.4.
When the spaetzle rise to the surface, about 1 minute later, cook for another minute or 2, then transfer with a slotted spoon or strainer into the bowl of ice water. Repeat until all the batter is used up. Drain the spaetzle (at this point, you can toss with a bit of olive oil and refrigerate, tightly covered, for up to a day).
For the stroganoff:1.
Put 2 tablespoons butter in a large skillet and turn the heat to medium-high. Season the steak with salt and pepper. When the butter foams, add the steak and cook, undisturbed, until it browns on the bottom and releases easily from the pan but is still blood-rare in the middle, 3-5 minutes. Turn and sear the other side, no more than 3 minutes. You want it a couple steps rarer than your ultimate goal. Transfer the meat to a cutting board and let it rest.2.
Add the onions to the pan; lower the heat to medium, and cook, stirring occasionally and adjusting the heat as necessary to prevent burning, until caramelized and jammy, 30-40 minutes. Stir in the mustard, tomatoes and stock. Bring to a boil, then adjust the heat so the mixture bubbles gently and cook, stirring once in a while, until it thickens a bit. Mix in the sour cream; taste, adjust the seasoning, and turn off the heat.3.
Meanwhile, put 2 tablespoons butter in another large skillet over medium-high heat. When the foaming subsides, add enough spaetzle to cover the bottom of the pan without crowding (you will have to work in batches; add some of the remaining 4 tablespoons butter with each batch). Adjust the heat so the dumplings sizzle without burning and cook, undisturbed, until the bottoms brown a little, 3-5 minutes. Toss with a spatula and cook until they're as golden and as crisp as you like, 3-5 minutes more.4.
Slice the meat thinly on the bias. If necessary, warm the onion mixture over medium heat until it's just beginning to bubble. Stir in the beef and any juices from the cutting board.
Divide the spaetzle among 4 shallow bowls, and spoon the stroganoff on top. Garnish with the dill and serve right away.