Bring a large pot of salted water to a boil. Add the pasta and cook until the pasta is al dente.Â
Before straining the pasta, remove 1.5 cups of starchy pasta water from the pot and set aside for later (we always take a little extra out just in case). Strain the water and set the pasta aside.Â
Heat a large skillet with sides over medium heat. Add olive oil.Â
When the olive oil is fragrant, add all of the mushrooms to the pan and toss with the olive oil until coated. Sprinkle the mushrooms with ½ teaspoon of the salt and toss.Â
Sauté the mushrooms for 5-7 minutes, tossing periodically until they are soft and start to brown.Â
Deglaze the pan (with the mushrooms still in the pan) with the white wine and scrape the bottom of the skillet pan to remove any brown bits.Â
Add the garlic, shallot, dried thyme, and the rest of the salt to the pan and sauté them with the mushrooms for 2-3 minutes.Â
Next, add the vegetable broth and ¾ of the starchy pasta water to the pan and mix all the ingredients together. Bring the liquid to a boil and then turn the heat to low and allow the mixture to simmer for 3-4 minutes.Â
Remove ¼ cup of the liquid from the pan and add the cornstarch to the removed liquid. Whisk the cornstarch and water together until it thickens (it should be almost a paste-like consistency).
Add the cornstarch slurry back into the saucepan and whisk it into the sauce. It should thicken the mushroom sauce almost immediately.Â
Finally, add the butter and lemon juice to the sauce and stir until the butter is melted. Â
Add the pasta to the skillet pan and toss until all the pasta is covered in sauce.Â
Top the pasta with the pecorino romano and fresh parsley.Â