The best fish sausage is made with both fatty and lean fish, but you can make it with only one or the other if you want. The oilier the fish, the quicker these sausages will get fishy, so keep that in mind.
500gramsdiced fatty fish,like salmon or tuna belly or trout
500gramslean white fish,cut into ¼-inch dice
21gramssalt,about 2 tablespoons
4gramswhite pepper,about 1 teaspoon
4gramsground anise seed or fennel seed,about 1 teaspoon
6gramswhole anise or fennel seed,about 2 teaspoons
4tablespoonschopped chives
4tablespoonschopped parsley or lovage
Sheep casings
Instructions
Soak the sheep casings in warm water to rehydrate.
Heat the butter in a pan over medium heat and sauté the minced onion until soft and translucent, but without browning it, about 8 minutes. Turn off the heat and let this cool, then refrigerate the onions. You want them cold before proceeding.
Put the salmon or other fatty fish into a food processor, along with a handful of crushed ice. Process into a fluffy puree, about 1 minute or so. Move this to a large bowl.
Add all the remaining ingredients, along with the cooled onions and any butter you can scrape from the bowl, and mix well with your (very clean) hands until it all comes together in one big ball. This should take about 90 seconds to 2 minutes of kneading and mixing.
Put this mixture into a sausage stuffer and thread the sheep casings onto the funnel. Fill the casings, erring on a little looser than tighter, as sheep casings are fragile. If you break one, move the fish mixture away from the break so you can tie it off, then continue with a new coil. It happens.
When you have the mixture all stuffed, you will want to pinch off links. I like links in sheep casings about four to five inches long. To do this you can tie them off with string, or pinch down with your fingers to make two links – the end link and the one between your fingers. Spin the link between your fingers away from you to tighten the link. You may see air pockets forming underneath the casing; we’ll deal with them in a bit. Now move down the coil and pinch off another two links. This time you spin the link towards you. Repeat this process, away from you, then towards you, all the way down the coils. (Here's a video showing you this process.)
When you are done, gently compress the fish mixture in a link at the end, then tie off that link. Do the same on the other end. Now get a needle or a sausage pricker and set the point in a burner until it glows; you are sterilizing it. Us this to prick every air pocket you can find in the links. When you get them all from a link, rotate it in the direction it was made (toward or away from you) to compress the meat into the link and seal up any air pockets.
Put your links in the fridge, uncovered, for up to a day. This tightens them and allows the links to bloom a bit. They will keep for a few days in the fridge and freeze well. I generally grill or pan fry them and serve with a seasonal salad.
Notes
If you want, you can make this fish sausage into patties instead of linking them. If you do this, they will be like high-class fish cakes.