Cook the fettuccine according to the directions on the package. While the pasta is cooking prepare the mushroom sauce.
In a large pan, melt 1 tablespoon of butter with 1 tablespoon of olive oil over medium heat. Once melted, add in the shallots and garlic and cook for a few minutes or so, just until softened.
Add in the sliced mushrooms and toss them around to get them coated in the butter and olive oil. If needed, add an additional tablespoon of olive oil if the mushrooms get too dry. Let them cook and brown for about 8 minutes.
Pour in the balsamic vinegar and stir everything together making sure to scrape up all of the browned bits on the bottom of the pan. Add in the other tablespoon of butter. Cook everything together for a couple of minutes and then turn off the heat and move the pan off the burner.
Pour in the cream and parmesan cheese and stir to combine.
Add the cooked fettuccine to the sauce and toss to combine. Add in the fresh parsley and season to taste with salt and pepper (about a ½ teaspoon of each).
Serve with additional parmesan cheese sprinkled over the top.
Credit: Girl Gone Gourmet, Jan. 4, 2015 - http://www.girlgonegourmet.com/2015/01/balsamic-mushroom-pasta.html