In a pot add olive oil, sliced onion, crushed red pepper flakes, salt, and cracked black pepper. Saute that on a medium heat for about 5 - 10 minutes or until the onions are golden brown. Then, add in the sliced garlic and saute that together for another few minutes.
Next, pour in the whole peeled tomatoes and mash them up using a wooden spoon or a potato masher. Once they are mashed up, bring the pot to a boil. Once the pot comes to a boil, pour in the marinara sauce and fill the empty jar up with a ½ cup of water. Swish the water around in the jar to get all the excess marinara out and add it into the pot. Give that a stir, add in more salt and cracked black pepper (if needed), and bring the pot back up to a boil.
Then, drop the heat to low and add in the stick of butter. Give that a stir and place the lid on the pot. Let that simmer on a very low heat for about 45 - 60 minutes.
Once your sauce is almost done simmering, bring a pot of water to a boil, salt the water, add in your pasta of choice (I used spaghetti), and boil the pasta until al dente. Once you begin boiling your pasta, move the lid that's covering the pot of sauce, and leave it slightly ajar for the remaining simmering time.
Serve the sauce over the pasta and garnish it with pecorino romano cheese. Enjoy!
