Warm 2 tablespoons of water to blood temperature — just past lukewarm – and mix the yeast and salt into it. Leave in the warm to froth.
Heat the butter in a small pan with the rosemary until the butter starts to brown. Add the sugar and then the warmed milk.
When this has cooled to lukewarm, strain on to the yeast in a large bowl, and add the granary flour. Mix to a dough.
Roughly chop the walnuts and add them to the dough, kneading to incorporate.
Cover the dough with a clean cloth or sheet of cling film and leave in a warm, draught-free spot to prove.
When the dough has roughly doubled in bulk, perhaps an hour or two, knock it back, i.e. knead it a couple of times to deflate it.
Shape into small baguettes and place on an oiled baking sheet. Leave to prove once more. When the loaves have doubled in volume, after about another 30 minutes, bake in an oven preheated to 400°F (200°C) Gas 6 for 15 minutes. They should be well browned, sound rather hollow when tapped and feel light when lifted.
As with most baking you may complete every step up to the second proving (step 7) quite well in advance and leave the bread in a fridge, covered with a cloth or cling film, until you want to bake it.