Cook the pasta to al dente in heavily salted water per the package directions. Right before draining, scoop out and save about a cup of the cooking water.
Meanwhile, preheat a large skillet to medium-high heat with a drizzle of oil. Add the mushrooms with a sprinkle of salt and saute for five minutes.
Add the shallots to the pan and stir for five minutes more to soften.
Add the butter to the pan and sprinkle the flour over the mushrooms. Stir to coat for one minute, then very slowly drizzle in the milk or half and half to create a bubbly sauce. Turn the heat down if the sauce bubbles very aggressively.
Add the pasta, 1 cup of grated parmesan cheese, and a splash of pasta water to the sauce. Stir to combine.
At this point, adjust! Add salt and pepper, more pasta water or parmesan, and stir a few times until the pasta is coated but not soupy and the sauce tastes great.
Serve with extra parm and black pepper. Enjoy!