Pasta with salmon

So I like to read the New York Times food section quite a bit, and a while ago read this post on braising pasta. I never measure the amounts of water (even though I know it's supposed to be quite a bit) when cooking pasta: I usually just pour water into a pan, and then shake some pasta in. I also read another post (can't remember where) about pasta water, especially from restaurants (who often use the same water to cook different batches) and how someone should really get into the business of bottling pasta water. Its starchy, thick, and has a great flavor one can use in sauces. So I bought some lovely salmon (on sale) yesterday, and also some Grana Padano (also on sale) this weekend and decided to make a salmon pasta in a mustard sauce. Using the pasta water. Except instead of just water, I used half homemade chicken stock (I keep freaking out that it's going to spoil) and half water. It was really, really good. And little cleanup as well.

Braised Pasta with Caramelised Onions and Salmon in Mustard sauce
3 large onions
200 g pasta (I used macaroni shaped pasta, but you could probably use orichette or penne)
350 g fresh salmon fillet (no skin and deboned) cut into chunks
2 tbs mustard (I used green pepper Maille brand)
1 tsp old bay seasoning
generous pinch salt
1-2 large cloves of garlic minced finely
40 g grated grana padano
About 500 ml chicken broth and 500 ml water

slice the onions into 2 cm thick half moons
Heat a saucepan, and on medium high heat, begin to caramelise the onions (throw them in, and don't disturb them for about 2 minutes. Then stir them around, and leave them alone again. This should take about 30 minutes, after which your onions should be a woody brown. If you want a darker brown, keep going)
Bring the chicken broth and water to a boil, and throw in the pasta. Reduce the heat to medium high and cook about 7 minutes
Prepare the salmon and the garlic and the cheese
Push the onions to the sides of the pan
Pour the noodles and cooking water in, and scrape up any brown bits from the bottom
Add the mustard, old pay, salt, garlic, and salmon, and stir gently to combine everything
Let simmer, stirring occasionally, 5 minutes or so until salmon is just cooked through
Top with cheese