Bring a large pot of salted water to boiling, then add fettuccine and cook according to package directions until al dente—don't oversoak it into mush. I always test a strand at 90% of the recommended time because pasta continues softening once you drain it.

While water heats, slice mushrooms into quarter-inch pieces and mince your garlic; uneven sizing means some pieces turn to paste while others stay firm. This feels like busy work, but uniform sizing prevents texture chaos later.

Heat olive oil and butter together in a large skillet over medium-high heat until the butter foams—this combination prevents pure butter from burning. When it stops actively bubbling (about 45 seconds), add diced onion and cook for 3-4 minutes until translucent, stirring twice.

Add minced garlic and sliced mushrooms, cooking for 5-6 minutes without moving them constantly—let them make contact with the hot pan so they brown instead of steam. You'll know it's ready when the mushrooms release their liquid and that liquid mostly evaporates; trust your nose here because you're building the umami foundation.

Pour in vegetable broth and dried thyme, then simmer for 3 minutes to marry those flavors before cream enters the picture. This step seems small, but it's the reason your creamy mushroom pasta crowd summer recipe tastes intentional instead of rushed.

Reduce heat to medium-low and stir in heavy cream slowly while stirring—rushing this step causes the sauce to break or separate. Once combined, add Parmesan, salt, and black pepper; the sauce should move like honey on a plate, not like soup.

Drain pasta and add it directly to the skillet, tossing gently for 1-2 minutes so the noodles absorb sauce instead of sitting on top of it. You want the pasta coated, not swimming—if it looks too thick, a splash of reserved pasta water loosens it without breaking the emulsion.

Taste and adjust seasoning (you may want more Parmesan), then serve immediately while the crowd mushroom pasta still holds that just-made warmth.