Bring a large pot of water to a boil. Salt generously. Add the pasta and cook until al dente. Reserve about a cup of the pasta water before draining.

Cut the rind from the brie and discard. Cut the cheese into pieces.

Dice the bacon into bite sized pieces. Heat a large skillet or Dutch oven over medium heat and add the bacon. Cook until crisp. Remove the bacon with a slotted spoon to a paper towel lined plate, reserving the bacon grease in the pan.

To the pan and the grease, add the onion. Cook until soft.

Add the cooked pasta to the pan, along with the cubes of brie. Stir, allowing the cheese to melt. Add enough of the pasta water to form a smooth sauce. (I usually use about 1/2 cup of water.)

Stir in the parmesan cheese, red pepper flakes, and the bacon. Season with lots of pepper and salt, if needed.