First, combine the flour, a teaspoon of salt and water. Add water, a splash at a time, until the flour comes together into a soft, workable dough.
Knead that until it starts to spring back - about 10 minutes - then rest it in the fridge for at least an hour. At this point, get some butter out of the fridge to allow it to warm up to room temperature.
Remove it from the fridge and roll it out until it's just a few MM thick, then layer slices of butter all over one half. Fold it over, then roll it out a little and repeat the process, folding it in half and rolling it out again and again, until you've created a very well layered, very consistent puff pastry dough.
Rest that in the fridge for another hour. While it rests, remove the sausage casings and mix the sausage meat together, adding any extra seasoning you might like to add. Pre-heat the oven to 200c.
Roll out the dough into a fairly long strip. About as wide as you want the sausage rolls to be long. Although you can and should trim the excess at this stage. Separate into 3 or 4 pieces and add sausage meat all the way across the width of each, then brush the pastry with water to make it stick and roll it over, wrapping it around the sausage.
Brush egg wash or milk over the top and then make a series of slices all the way through the pastry in the top to allow any steam to escape while it cooks. Place it in the oven for 30 minutes. During the last 5 - 10 minutes, take a look to see how it is browning up. If it still looks too light, increase the heat up to anywhere from 220c to 240c.