Bring a pot of water to a boil. Add about a tablespoon of salt to the boiling water. Cook the pasta al dente, according to package instructions.
Drain the pasta, reserving a cup of pasta water to be used in the sauce. Set the cooked pasta and reserved pasta water aside.
In a large skillet over medium-high heat, add the oil and butter.
Add mushrooms and cook until tender, 8-10 minutes, stirring occasionally. Add the garlic, salt, and pepper and cook for one minute.
Transfer the mushrooms to a bowl and set them aside.
To the same skillet you cooked the mushrooms, add the shrimp and champagne. Cook over high heat until the champagne begins to boil, 3-5 minutes, stirring occasionally.
After the liquid has come to a boil, use a slotted spoon to remove the cooked shrimp from the skillet. Add the shrimp to the bowl of mushrooms.
Add the shallots and tomatoes to the skillet. Boil until the liquid (champagne) has been reduced to about ½ cup, approximately 8-10 minutes.
Pour in the heavy cream. Boil for 1-2 minutes, or until the sauce thickens. If the sauce is not thick enough, add some reserved pasta water to it (starting with ¼ cup) until it reaches your desired consistency.
Add the mushrooms and shrimp to the sauce. Cook until heated through. Add parsley. Salt and pepper to taste.
Place the pasta on a plate and top with the mushroom and shrimp sauce. Serve garnished with additional parsley.