Tomato Sauce with Onion, Butter, Marjoram

After reading through several recipes for various tomato sauces, I ended up with the following:

2 cups canned imported Italian plum tomatoes, cut up w/ juice
4 TBSP butter
1/4 onion, peeled
1 tsp marjoram
salt
2 oz. spaghetti

Put the tomatoes, butter, onion (all in once piece), marjoram and salt in a saucepan and cook uncovered at a slow but steady simmer for 45 minutes. Stir from time to time, mashing the larger pieces of tomato. Taste and correct for salt. Discard the onion before tossing with cooked pasta. Serve with parmesan cheese on the side.

Notes: I've done one other similar style approach in the past. That one came out rather well, but this was not quite as good; the sauce was a little on the oily side. I would've liked this one to be a bit thicker and creamier (so more experimentation is called for). But it tasted very good.