Bring a large pot of salted water to a rolling boil and cook the pasta according to package instructions until al dente, about 8–10 minutes.

In a wide skillet, heat olive oil over medium heat, add the sliced leeks with a pinch of salt, and cook for 10 to 12 minutes until golden brown.

Add butter and sliced mushrooms to the skillet, sauté for 5 to 7 minutes until golden brown, then stir in minced garlic and thyme.

Pour in vegetable broth, scrape up browned bits, and let simmer for a minute before stirring in heavy cream.

Add shredded Gruyere cheese into the sauce, stirring until melted. Adjust consistency with reserved pasta water if necessary; season with salt, pepper, and lemon juice.

Toss cooked pasta in the creamy sauce until evenly coated, cooking for another minute before serving.