Start by preparing everything before you turn on the heat. Slice the mushrooms evenly so they cook at the same rate. Finely dice the onion and chop the garlic. Having everything ready will make the cooking process smooth and controlled.
Bring a large pot of water to a boil and season it generously with salt—it should taste like the sea. Add the pasta and cook until al dente. Before draining, reserve about 1 cup of pasta water. This starchy water is key for adjusting and binding your sauce later.
Heat butter in a large pan over medium-high heat. Once hot, add the mushrooms in a single layer. Do not stir right away—let them sit so they can develop a deep golden color. This step builds the foundation of flavor.
Add the diced onion to the pan and cook until soft and slightly translucent. Then add the chopped garlic and cook briefly, just until fragrant—be careful not to let it burn.
Pour in the white wine and let it simmer for 1–2 minutes. Use a spoon to gently scrape the bottom of the pan, lifting all the flavorful bits. Allow the wine to reduce slightly so the flavor becomes more rounded and less sharp.
Lower the heat and add the cream. Let it simmer gently for a few minutes until it thickens slightly. Season with salt and freshly ground black pepper. Keep the heat controlled—too high and the cream can split.
Add the cooked pasta directly into the pan. Pour in a small splash of the reserved pasta water and toss everything together. The starch from the pasta water will help create a smooth, silky sauce that coats the pasta evenly. Add more water if needed to reach the right consistency.
Stir in the grated Parmesan and allow it to melt gently into the sauce.
Turn off the heat and add the fresh parsley. Give everything a final toss, then taste and adjust the seasoning if needed. Serve immediately while the pasta is hot, creamy, and perfectly coated.