Bring a large pot of salted water to a rolling boil. Add the pasta and cook until al dente, about 8-10 minutes. Reserve ½ cup of pasta water, then drain the pasta.

In a large skillet, heat olive oil over medium heat. Add sliced leeks and a pinch of salt, cooking for 10-12 minutes until soft and golden.

Add butter to the skillet with the leeks, then add sliced mushrooms. Brown the mushrooms undisturbed for 5-7 minutes.

Stir in minced garlic and thyme, cooking for 1 minute until fragrant.

Pour in vegetable broth, scraping the bottom of the pan. Simmer for 3-4 minutes.

Stir in heavy cream, allowing the sauce to thicken for about 5 minutes.

Gradually add Gruyere cheese, stirring until melted. If needed, add reserved pasta water for desired consistency.

Add the cooked pasta to the skillet, tossing with the sauce. Season with salt, pepper, and lemon juice before serving.