Follow these steps carefully to achieve the most delicious Creamy Mushroom Pasta:

1. Cook the Pasta: Bring a large pot of salted water to a rolling boil. Add your chosen pasta and cook according to package directions until al dente (tender but still with a slight bite). Before draining, reserve about 1-2 cups of the starchy pasta water. Drain the pasta and set aside. Tossing it with a tiny drizzle of olive oil can prevent sticking if it will sit for a few minutes.
2. Sauté Aromatics: While the pasta is cooking, heat the butter and olive oil in a large, heavy-bottomed skillet or Dutch oven over medium heat. Once the butter is melted and foamy, add the finely chopped onion. Sauté for 4-5 minutes, stirring occasionally, until softened and translucent. Add the minced garlic and cook for another minute until fragrant, being careful not to burn it.
3. Cook the Mushrooms: Increase the heat slightly to medium-high. Add the sliced mushrooms to the skillet. It might seem like a lot, but they will cook down. Spread them in a relatively even layer and cook without stirring for 3-4 minutes, allowing them to get some good browning on one side. This develops their deep, umami flavor. Then, stir and continue to cook for another 5-7 minutes, or until they are nicely browned, have released their liquid, and that liquid has mostly evaporated. Season the mushrooms with a pinch of salt and freshly ground black pepper.
4. Deglaze (Optional but Recommended): If using white wine, pour it into the skillet. Scrape up any browned bits from the bottom of the pan with a wooden spoon – these bits are packed with flavor! Let the wine simmer and reduce by about half, which should take 2-3 minutes. If not using wine, you can use a splash of the vegetable broth for this step.
5. Build the Creamy Sauce: Reduce the heat to medium-low. Pour in the heavy cream and vegetable broth. Bring the mixture to a gentle simmer, stirring occasionally. Allow it to simmer for 3-5 minutes, or until the sauce begins to thicken slightly.
6. Add Cheese and Seasoning: Stir in the freshly grated Parmesan cheese until it melts and the sauce becomes smooth and even creamier. Taste the sauce at this point and adjust seasoning with salt and pepper as needed. Remember that Parmesan is salty, so you might not need much additional salt.
7. Combine Pasta and Sauce: Add the cooked pasta directly to the skillet with the sauce. Toss everything together gently but thoroughly to ensure every strand of pasta is coated in the glorious creamy mushroom sauce. If the sauce seems too thick, add a splash of the reserved pasta water, a little at a time, until it reaches your desired consistency. The starchy pasta water helps the sauce emulsify and cling beautifully to the pasta.
8. Finish and Serve: Stir in most of the chopped fresh parsley, reserving a little for garnish. Serve the Creamy Mushroom Pasta immediately in warm bowls. Garnish with the remaining fresh parsley and an extra sprinkle of freshly grated Parmesan cheese. A crack of black pepper on top is also lovely.