In a large, heavy pan over medium heat, warm the olive oil and butter.
Add the onion and garlic and sautué until golden and fragrant, about 2 minutes.
Add the mushrooms and sautué, stirring with a wooden spoon, until they begin to soften, 3 to 4 minutes. Increase the heat to high, add the wine or stock and thyme.
Cook, stirring constantly, about 3 minutes. Reduce the heat to low, season with salt and pepper and continue to cook, stirring often, until the mushrooms are cooked through and all the liquid has evaporated, about 15 minutes more. Add the fresh basil.
Meanwhile, bring a large pot with water to a boil over high heat. Salt the boiling water, add the pasta and cook until al dente, about 8 minutes. Drain, reserving about ¼ cup of the cooking water.
When the mushrooms are ready, remove from the heat. Add the pasta and toss, adding the reserved cooking water if the pasta seems too dry. Serve with a green salad