Begin by bringing a large pot of salted water to a rolling boil. Add your choice of long pasta, like spaghetti or fettuccine, and cook for about 8 minutes or until al dente, following package instructions. The pasta should be firm yet tender to the bite. Once done, drain it, making sure to reserve a small cup of the cooking water for later.

In a large sauté pan, melt a tablespoon of butter over medium-high heat. As the butter starts to foam, add sliced mushrooms and fresh thyme. Sauté these for about 4 minutes or until the mushrooms soften and lightly caramelize, releasing their delightful umami flavor. This aromatic mixture sets a robust base for the rich sauce.

Add the bone marrow to the pan with the sautéed mushrooms. Season generously with salt, pepper, and a splash of lemon juice for brightness. Cook this mixture for about 3 minutes, stirring frequently. You'll know it's ready when the marrow is melted and the entire mixture is warm and fragrant.

With the sauté mixture ready, gently fold in the drained pasta, ensuring it absorbs all the luscious flavors. Next, add freshly grated Parmigiana cheese and a generous dollop of creme fraiche, stirring continuously. If needed, incorporate some reserved pasta water to achieve your desired sauce consistency.

Taste the dish and adjust seasoning with more salt, pepper, or lemon juice as necessary. Continue to stir on low heat for a minute to meld all the flavors together fully.

To finish, plate your Bone Marrow Pasta generously in warm bowls. If desired, sprinkle with extra Parmigiana cheese and a few sprigs of fresh thyme for added flair. Serve immediately while hot.