Can I make tajarin with dried porcini?

Yes, dried porcini work well and have a concentrated flavor. Soak them in hot water until soft, strain the liquid carefully, and use a little of it in the sauce.

What pasta can I use instead of tajarin?

Fresh tagliolini is the closest easy substitute. Fresh egg tagliatelle also works, though its wider ribbons will give the dish a different texture.

Do I need to rinse fresh porcini mushrooms?

No, brush fresh porcini clean with a damp towel instead. Rinsing can leave them wet, which makes them steam rather than brown.

Can I make this pasta ahead?

The mushroom sauce can be made a few hours ahead and refrigerated, but cook the tajarin just before serving. Reheat the sauce gently and loosen it with pasta water.

Tajarin with Porcini Mushrooms

Symptom	Cause	Fix
The mushrooms look pale and watery.	The pan was crowded, or the mushrooms were rinsed and went into the pan wet.	Brush fresh porcini clean, dry them well, and cook in batches so moisture can evaporate.
The garlic tastes bitter.	It browned while the mushrooms were cooking.	Add the sliced garlic only after the mushrooms have browned, and cook it briefly.
The sauce is greasy or clumps around the noodles.	The pasta was tossed with butter without enough starchy water, or the skillet was too hot.	Lower the heat and toss in pasta water a tablespoon at a time until the sauce lightly coats the noodles.
The tajarin turn mushy.	Fine fresh noodles cook quickly and were left in the water too long.	Check them early, follow the package timing, and drain as soon as they have a slight firm bite.
The dried porcini taste gritty.	Sediment from the soaking liquid made it into the sauce.	Lift the mushrooms out and strain the liquid slowly through a coffee filter or a fine-mesh strainer lined with paper towel.

Method

1
If using dried porcini, cover them with 1 cup (240 ml) hot water and soak for 20 minutes, until soft. Lift them out, strain the soaking liquid through a fine-mesh strainer lined with a coffee filter, and reserve it. Slice the porcini. If using fresh, brush off any dirt with a damp towel and slice them; do not soak them.
2
Bring a large pot of water to a boil. Add the salt. Keep the water at a steady boil while you make the mushroom sauce.
3
Heat the olive oil and 2 tablespoons (28 g) of the butter in a wide skillet over medium-high heat. Add the mushrooms in a single layer, working in batches if needed. Cook fresh porcini for 6 to 8 minutes, or rehydrated porcini for 3 to 4 minutes, stirring occasionally, until tender and browned at the edges.
4
Add the sliced garlic and cook for 30 seconds, just until fragrant. Pour in the wine and simmer for 1 to 2 minutes, until reduced by about half. If using dried porcini, add ⅓ cup (80 ml) of the reserved soaking liquid and simmer for 2 to 3 minutes. Turn off the heat while the pasta cooks.
5
Add the tajarin to the boiling water and cook according to the package directions, usually 1 to 3 minutes for fresh noodles. Taste a strand; it should be tender with a slight firm bite. Before draining, scoop out 1 cup (240 ml) of pasta water.
6
Return the skillet to low heat. Add the drained pasta, the remaining 2 tablespoons (28 g) butter, and ¼ cup (60 ml) pasta water. Toss for about 1 minute, adding more pasta water a tablespoon at a time until the butter forms a light coating on the noodles.
7
Turn off the heat and toss in the parsley. Taste and adjust the salt. Divide among warm bowls and serve at once with grated Parmigiano-Reggiano.