Boil water for the tortellini and cook it according to package instructions.
Meanwhile, prep the mushrooms and the sage.
When the tortellini is about 6-7 minutes from being ready (so a bit before you add it to the boiling water), add 1 tbsp of the butter and the olive oil to a skillet over medium-high heat. When the pan is hot, add the sage. Cook it for about a minute until it crisps up. Take it out of the pan and set aside.
Add the mushrooms, garlic, and another tablespoon of the butter to the pan. Sauté for about 5 minutes, stirring occasionally, or until the mushrooms are nicely browned.
Add the drained tortellini, remaining butter, parmesan cheese, and sage to the pan. Toss until everything's nicely coated. Season with salt & pepper as needed. Serve immediately.
This recipe makes 3-4 servings. It is pretty rich, so I'd serve 4 but ensure there's other stuff to eat with it like a salad, or you could make 2 large portions.