Bring a large pot of salted water to a rolling boil over high heat. Add your choice of pasta, cooking it until al dente, usually around 8-10 minutes. Reserve half a cup of the starchy pasta water before draining the other half and set aside.

In a large skillet, heat 2 tablespoons of olive oil over medium heat. Add the sliced leeks along with a pinch of salt, stirring occasionally. Allow them to cook slowly for about 10-12 minutes, or until they’re beautifully golden and caramelized, giving off a sweet aroma.

Add 2 tablespoons of butter to the skillet with the caramelized leeks. Incorporate the sliced mushrooms and sauté for 5-7 minutes, stirring occasionally, until they are browned and tender.

Stir in 2 cloves of minced garlic and 1 teaspoon of fresh thyme leaves to the skillet. Cook for an additional minute, just until the garlic becomes fragrant.

Pour in 1 cup of vegetable broth and scrape up any flavorful bits from the bottom of the skillet. Allow the mixture to simmer for 3-4 minutes. Then, add in 1 cup of heavy cream and stir in the Gruyere cheese until it melts and creates a creamy sauce.

Finally, add the drained pasta to the skillet, tossing everything together until the pasta is evenly coated in the creamy Gruyere sauce. Adjust seasoning with salt, pepper, and a squeeze of lemon juice to brighten the dish.