Tomato Sauce with Butter & Onions

We had some frozen chantrelle mushroom raviolli in the freezer that we wanted to have for dinner last night. I found this recipe on Smitten Kitchen and thought it would be the perfect sauce to use. I couldn't believe how easy it was to make! I did add a few things, but even without them, this sauce was great! I have to give credit where credit is due--this picture was taken by my wonderfully talented husband! I think he takes better pictures than I do. I just might have to hire him to be my official food photographer! :)

28 ounce can Whole Peeled Tomatoes (I used San Marzano)
5 tablespoons Unsalted Butter
1 Yellow Onion, peeled and halved
*1 Garlic Clove, peeled and smashed (I added this)
*Dash of Dried Basil (I added this)
*Dash of Red Pepper Flakes (I added this)

Put the tomatoes, onion, garlic, and butter in a heavy saucepan over medium heat. Bring the sauce to a simmer and then lower the heat to keep the sauce at a slow, steady simmer for 45 minutes, or until droplets of fat free from the tomatoes. Stir occasionally, crushing the tomatoes against the side of the pot with a wooden spoon. At this point, I added the red pepper flakes and basil. Remove from heat and discard the onion. (I put the onion in the freezer to use in a stock at a later time).