Step 1

Place 1 1/2 cups boiling water and 1 ounce dried porcini mushrooms (about 3/4 cup) in a medium heatproof bowl and let soak for 20 minutes. Meanwhile, prepare the sauce ingredients.

Step 2

Prepare the following, placing them all in the same medium bowl: Mince 3 garlic cloves (about 1 tablespoon), dice 1 medium yellow onion (about 1 1/2 cups), peel and dice 1 large carrot (about 3/4 cup), and dice 2 medium celery stalks (about 1 cup).

Step 3

Place 1 pound fresh cremini mushrooms in a large bowl. Smash with your hands to create small (about 1/4-inch) crumbles (about 3 1/2 cups). Finely chop until you have 2 teaspoons fresh thyme leaves and 1 teaspoon fresh rosemary leaves, and add both to the bowl of mushrooms. If needed, finely grate 2 ounces Parmesan cheese (about 1 cup).

Step 4

When the dried porcini mushrooms are ready, drain but reserve the soaking liquid. Finely chop the mushrooms.

Step 5

Heat 3 tablespoons olive oil and 3 tablespoons unsalted butter in a large Dutch oven or heavy-bottomed pot over medium-high heat until the butter is melted. Add the garlic mixture and cook until the vegetables are softened, fragrant, and just starting to brown, 7 to 10 minutes. Add the cremini mushroom mixture, porcini mushrooms, 1 (14.5-ounce) can whole tomatoes with their juices, 3/4 teaspoon kosher salt, 1/2 teaspoon black pepper, 1/4 teaspoon red pepper flakes, and 1/4 teaspoon ground nutmeg.

Step 6

Reduce the heat to medium and cook, stirring often and smashing the tomatoes so they fall apart, until there is no liquid remaining in the bottom of the pot, the mushrooms are dark brown, and the pot has a few brown bits stuck to the bottom, 16 to 20 minutes. (At first it will look like the mushrooms have released a lot of liquid, but this is normal. The liquid will eventually cook off.) If the bottom of the pot starts to burn during cooking, add a tablespoon of the reserved mushroom soaking liquid and continue cooking. Don’t rush this part. The mushrooms need a long time to develop a savory flavor.

Step 7

Add 1/2 cup dry red wine and scrape up the browned bits on the bottom of the pot with a wooden spoon. Cook until the wine has almost completely evaporated, 1 to 2 minutes. Add the reserved mushroom soaking liquid (leave any mushroom sediment behind) and 1/2 cup whole milk. Reduce the heat to medium and cook, stirring occasionally, until the bolognese is thick, darkened in color slightly, and the liquid has reduced by half, 6 to 7 minutes. Meanwhile, bring a large pot of salted water to a boil over high heat.

Step 8

Add 1/4 of the grated Parmesan cheese to the sauce and stir until melted. Taste and season the bolognese with more kosher salt as needed. Reduce the heat to low to keep it warm. Add 1 pound dried fettuccine to the pot of boiling water and cook according to the package directions. Drain the pasta and add it to the bolognese. Turn the heat off and toss to coat the pasta. Serve immediately with the remaining Parmesan cheese and freshly cracked black pepper.