Bring a large pot of salted water to a boil. Add the pasta and cook until al dente. Reserve a mug full of the pasta water and drain.
Meanwhile, cook the bacon and onion until the bacon is crisp and the onion is tender. Add the cooked pasta to the bacon & onion. Add in the brie and stir to melt and combine. Add in enough of the pasta water to form a smooth sauce. Season generously with black pepper and serve with Parmesan cheese.
