Boil your water and add the pasta. Cook according to the instructions.
Add the olive oil and butter to a medium heat pan. Sautee the onions and garlic until fragrant. Add the red pepper flakes for an additional 30 seconds.
Pour in your heavy cream (I like to add a little extra - it makes it super creamy) and let this reduce for a couple minutes.
Once reduced, add in the pasta water and again let this simmer for about a minute. This gives the dish that extra shiny look and brings it all together.
Add in your cooked pasta and stir to combine. Top with extra parmesan if you'd like! Enjoy!