While this will be a better dish with fresh sardines and homemade pasta, quality tinned sardines and good store-bought dried pasta are almost as good. This is not a dish that keeps well. Eat it, enjoy it, and move on. Leftovers can get fishy.
Toast the pine nuts in a dry pan over medium-high heat until they smell nice and are slightly browned. Move to a bowl and set aside.
Pull the backbones out of all the sardines. It doesn't matter if they are a bit messy or if there are any teeny ribs or somesuch. They're going to get broken up anyway.
Bring a large pot of water to a boil and add a palm full of salt. If you have it, Put the tops of a fennel bulb, or, even better, a big bunch of wild fennel into the water and boil it for 15 minutes. Remove the fennel and discard. The idea is to perfume the pasta water. Once this is done, start boiling your pasta.
In a large pan, heat the olive oil over medium-high heat and add the onion and anchovies. Sauté, mashing the anchovies as you go. They'll dissolve into a paste. Add the garlic and sauté another minute, then all the sardines. Stir well and break up the sardine pieces. Cook about 5 minutes.
Add the saffron, pine nuts and capers and continue to cook until the pasta is ready. Move the pasta to the pan with the sauce, add the fennel and the lemon zest and juice and toss to coat. Grind some black pepper over it all and serve.
Notes
Keys to Success
Quality really matters here. Good sardines, fresh or tinned, good olive oil, fresh garlic and lemon, quality pasta. You will really taste the difference.
If you use salted anchovies, you need to rinse them first.
Don't use too much sauce. Big globs will come off fishy. A light coating is what you want.
Serve with a crisp white wine, like a Sancerre or Pinot Grigio or Albariño.
Variations
You can add a tablespoon or two of tomato paste with the anchovies.
You can substitute herring, smelt or other small fish for the sardines.