Heat oil/fat of choice on medium.
Chop guanciale in to ¼-inch bits. When oil is hot, add guanciale and fry until crispy. Remove and save. Add chopped onions and garlic sauté until soft and starting to brown. At this point you can add some red chili flakes and cook an extra minute or two.
Then add a ½ c. tomato puree, ½ c. water, mix, and let reduce a bit. Keep stirring you don’t want to burn or brown the tomatoes. When tomato mixture is dark, add ½ c. water and another batch of tomato. Repeat until all the puree is cooking. Turn heat down to low.
At this point the sauce should be reduced and a burgundy-ish color, add 1 cup of water (or more) and add meatballs. I used SeaBreeze Farm sausage by squeezing bits out of the casing and rolling into balls. (This sausage is seasoned in a very complementary way for this sauce. You can also make your own meatballs.
Once the sauce is at the desired thickness and the sausage is cooked through, mix in the guanciale. Serve on hot pasta with garnish of basil.
Variation: I had approximately 2 tbs of fromage blanc. I threw it in. I will now always add it to this dish. It helps smooth out the acidity of the tomatoes.
Note: Amatrice is a city in Italy known for their pasta sauce made with guanciale & pecorino. A more typical recipe can be found here: http://italianfood.about.com/od/meatsauces/r/blr1007.htm