1. Bring a large pot of salted water to a boil. Cook the pasta according to package directions until al dente. Reserve 1 cup of pasta water, then drain and set aside.
2. While the pasta cooks, heat 2 tablespoons of butter and 1 tablespoon olive oil in a large skillet over medium heat. Add the sliced leeks and a pinch of salt. Cook slowly, stirring occasionally, for about 15-20 minutes until the leeks are golden and caramelized. This step is key—slow and gentle heat brings out their natural sweetness.
3. Add the remaining 1 tablespoon olive oil to the skillet along with the mushrooms. Increase heat to medium-high and sauté until the mushrooms release their juices and start to brown, about 7-10 minutes.
4. Stir in the minced garlic and thyme, cooking for 1-2 minutes until fragrant.
5. Pour in the white wine, if using, and let it simmer for about 3-4 minutes until mostly reduced. This step adds a subtle acidity and complexity that Mama Lou swore by for flavor layering.
6. Lower the heat and stir in the heavy cream. Let the mixture simmer gently for 5 minutes, allowing the sauce to thicken slightly.
7. Add the grated Gruyère cheese gradually, stirring until melted and smooth. Season with salt, black pepper, and red pepper flakes if desired.
8. Toss the cooked pasta into the sauce, adding reserved pasta water a little at a time to loosen the sauce and help it cling beautifully to each strand.
9. Remove from heat and sprinkle with fresh parsley before serving.

A little secret I learned from Ouma is to taste as you go—adjusting seasoning and texture until it feels just right. Cooking isn’t about rushing; it’s about savoring every step, just like Mama Lou taught me.