First, roughly chop the walnuts and preheat the oven to 225 degrees top / bottom heat.
Dissolve the yeast in half a liter of lukewarm water while stirring. Mix the flour and salt. Add the yeast water, walnuts and vinegar. Knead with a hand mixer for 3 minutes. The dough is very soft and must therefore be filled immediately into a loaf pan lined with baking paper. The dough does not need to rise in spite of the yeast cube.
Bake the bread on the lowest rack for 30 - 35 minutes, then leave it to stand in the switched-off oven for another 5 minutes. Then let the bread cool down on a rack.
You can bake the bread with other nuts if you like.