In a large sauté pan over medium heat, add 2 tablespoons of olive oil and 2 tablespoons of butter. Once melted, toss in the sliced leeks and sprinkle them with ½ teaspoon salt and ½ teaspoon granulated sugar. Cook the leeks for about 20 minutes, stirring occasionally, until they are golden brown and caramelized. If they start to stick, add a splash of water to keep them moist.

Next, add the remaining 2 tablespoons of butter and 8 ounces of oyster mushrooms to the same pan. Spread the mushrooms out in an even layer and allow them to brown for about 5-7 minutes. Remember to season with salt and pepper to taste. Once they are beautifully golden, remove the pan from heat momentarily to allow flavors to meld.

Return the pan to the heat and stir in 4 cloves of minced garlic and 2 sage leaves. Sauté for 1 minute, allowing the garlic to become fragrant and slightly golden, but be careful not to burn it.

Pour in ¾ cup of heavy cream, 1 tablespoon of balsamic vinegar, and 1 teaspoon of lemon zest to the pan, stirring everything together. Let the mixture simmer for 2-3 minutes, allowing the sauce to thicken slightly. Taste and adjust the seasoning with salt and pepper.

While the sauce is simmering, boil a large pot of salted water and cook 1 lb of fettuccine until al dente, about 8-10 minutes. Be sure to reserve 1 cup of the pasta water before draining the fettuccine.

Once the fettuccine is cooked and drained, add it to the sauté pan with the sauce. Pour in the reserved pasta water gradually, tossing everything together. Then, fold in ½ cup of grated Gruyere and sprinkle with 1 teaspoon of black pepper.

Finally, dish out the Caramelized Leek and Mushroom Gruyere Pasta into bowls. Top with ¼ cup of toasted pine nuts for an added crunch and extra layer of flavor. Serve it immediately.