Step 1

Fill a large pot with water and 1 tablespoon oil; bring to a rolling boil. Stir in tortellini and cook until they float to the top and the filling is hot, about 7 minutes. Drain and transfer to a large bowl.

Step 2

Meanwhile, melt 2 tablespoons of butter in a large saucepan over medium-high heat. Saute mushrooms, onion, and garlic until the vegetables are soft, about 5 minutes. Use a slotted spoon to remove vegetable mixture from the pan and add it to the bowl with the tortellini.

Step 3

Drain the excess liquid from the mushrooms from the saucepan. Reduce heat to medium and melt remaining 6 tablespoons butter. Stir in half-and-half, salt, pepper, garlic powder, and cayenne. Cook, stirring occasionally, until thick and bubbly, about 10 minutes. Gradually stir in Parmesan cheese until melted and sauce has thickened.

Step 4

Pour the sauce over the tortellini and mushroom mixture, and toss to combine. Serve in bowls and garnish with fresh thyme.