Fresh Tomato Sauce

I found this recipe while reading the NYT at work a while ago when I was drowning in CSA tomatoes.
I swapped the canned tomatoes out in favor of my fresh tomatoes, and employed an immersion blender which results in a frothy, creamy, thick, bright orange -- and SUPER DELICIOUS -- sauce.

yield: sauce for 1 lb of pasta

ingredients
2 lbs fresh tomatoes, diced
5 tbs salted butter, cold
1 onion, diced
2 tsp sea salt (more as needed)

directions

1. Combine tomatoes and their juices, butter, salt, and onion in a large saucepan. 
2. Bring to a simmer over medium heat.
3. Cook, uncovered, for 45 minutes; stir occasionally.
4. Puree with an immersion blender until smooth.
5. Enjoy!