Preparation

Make the shallot marmalade:

• Melt the butter in a 3-quart saucepan over medium heat. Add the shallots and cook, stirring occasionally, until translucent, 3 to 5 minutes. Add the sugar and vinegar, reduce the heat to medium low, and cook, stirring occasionally, until thickened, about 15 minutes.

Make the spaetzle:

• Bring a large pot of salted water to a boil over high heat. Have ready a large bowl of ice water.
• Purée the sour cream, milk, eggs, salt, and cracked pepper in a blender until smooth. Pour the mixture into large bowl and fold in the flour.
• To cook the spaetzle, place a spaetzle maker over the boiling water. Push the dough through the holes, letting it fall into the water below. (If you don’t have a spaetzle maker, use a rubber spatula to push the dough through the holes of a colander set over the pot of water.) The dough will form small dumplings as it drops into the water. Allow the spaetzle to rise to the surface and float for about 30 seconds before transferring it to the ice water with a slotted spoon. Let cool completely, about 5 minutes. Drain well, transfer to a large bowl, toss with the oil, and reserve.

Cook the mushrooms:

• Heat the oil in a 12-inch skillet over high heat until very hot. Add the mushrooms and cook, stirring often, until softened, 5 minutes. Add the shallots, garlic, and thyme. Reduce the heat to medium and cook, stirring occasionally, until the mushrooms are tender, about 3 minutes. Stir in the sherry vinegar and continue to cook until the pan is almost dry, about 1 minute.
• Take the pan off the heat and drizzle in the truffle oil (if using). Season to taste with salt and pepper, and a touch of vinegar, if necessary. Keep warm.

Grill the steaks and serve:

• Season the steak generously with salt and pepper. Heat a grill pan (or a large cast-iron skillet) over medium-high heat until very hot. Working in batches if necessary, grill the beef until medium rare (130°F to 135°F on an instant-read thermometer), 2 to 3 minutes per side. Transfer to a cutting board and let rest for 5 minutes.
• In a small bowl, combine the crème fraîche and 1/2 tsp. each salt and pepper.
• Melt the butter in a 12-inch skillet over medium-high heat. Add the shallot marmalade and cook until heated through and thinned, about 2 minutes. Add the spaetzle and the mushrooms; cook, stirring, until heated through, 2 to 3 minutes.
• Thinly slice the steak across the grain. Serve the steak over the spaetzle, drizzled with the crème fraîche and garnished with the dill sprigs.

Make Ahead Tips

You can make and refrigerate the marmalade up to 1 week ahead; it will become very thick as it cools. The spaetzle can be made up to 1 day ahead. Refrigerate in an airtight container.

If you can’t find black trumpets, use portobellos instead.