Bring a large pot of salted water to a rolling boil over high heat. Add pasta and cook according to package instructions until al dente, about 8 to 10 minutes. Reserve ½ cup of the starchy pasta water before draining.

In a skillet over medium heat, drizzle in olive oil. Add sliced leeks and a pinch of salt. Sauté for 10 to 12 minutes until softened and golden brown.

Add butter and sliced mushrooms to the skillet. Cook for about 5 to 7 minutes until browned and drained of moisture.

Stir in minced garlic and thyme. Cook for 1 minute until garlic is fragrant.

Pour in white wine, scraping the browned bits from the skillet. Let simmer for 2 minutes to evaporate alcohol.

Reduce heat and stir in heavy cream. Simmer until thickens slightly and coats the back of a spoon.

Toss in shredded Gruyere cheese, stirring until melted. Gradually add reserved pasta water to achieve desired sauce consistency.

Season sauce with salt, pepper, and lemon juice. Add cooked pasta, tossing gently until coated.