2 tablespoons unsalted butter
1 large onion, chopped into matchsticks
4 fat cloves garlic, minced
8 cups mushrooms, any variety, cleaned, washed and sliced (recommended: a blend of shitake, enoki, porcini and portobello)
2 tablespoons fresh sage, minced, divided
1 1/2 cups chicken stock
1 pound spaghetti
2 1/2 tablespoons truffle paste
1/3 cup cream
Salt to taste
Fresh ground pepper
Pecorino Romano, grated for garnish
Boil water with plenty of salt for the spaghetti.
Over medium-high heat, in a large frying pan, heat oil and butter. Saut onion for 2-3 minutes, until opaque. Add minced garlic, and cook for about one minute, stirring constantly, being careful not to burn it. Mix in mushrooms. (It may seem like a lot in the pan, but the mushrooms will reduce eventually. Also if it seems like the oil and butter are absorbed too quickly by the mushrooms, dont worry, add another tablespoon or so of olive oil). Cook 3-5 minutes, adding a pinch of salt in the last stages.
Add half of the sage, increase to high heat and add chicken stock. Bring to a boil, then reduce heat and simmer for 8 minutes.
At this point, drop the spaghetti into the boiling water and cook for 8 minutes. Note: Do not cook it for the recommended 12 minutes, because it should be undercooked when it goes into the ragu.
After the mushroom mixture has been simmering for 5 minutes, add truffle paste and simmer for another minute. Add cream and simmer 2 minutes.
Pull the pasta from the cooking water with tongs, placing it directly into the sauce. Add remaining sage, salt and pepper to taste and simmer for 2 more minutes. If the ragu seems dry, add some of the starchy pasta cooking water as needed. Serve immediately and garnish each bowl with freshly grated Pecorino Romano.