Step 1

Cook the pasta according to its package directions. Before draining the pasta, reserve one cup of the starchy cooking water.

Step 2

As the pasta cooks, make the mushroom sauce. Place a large skillet over medium-high heat. Add the butter and olive oil. Once the butter is melted, add the mushrooms. Cook for five minutes, stirring occasionally.

Step 3

Add the onions to the skillet. Cook for five minutes, stirring occasionally, until the onions are soft and the mushrooms are dark.

Step 4

Add the garlic, salt, time, and pepper. Cook for two minutes, stirring often.

Step 5

Remove the skillet from the heat. Slowly and carefully add 1/4 cup of the reserved water. Stir and scrape up any brown bits from the bottom of the skillet.

Step 6

Add the mushrooms and the Parmesan cheese to the cooked and drained pasta. Stir well.

Step 7

If the pasta looks a little dry, add more cooking water.