Peel the celeriac and parsnip and chop them both into bite-size pieces
Crush the garlic or chop it very fine
Slice thinly about 2 cm of the bottom of the leek - save the rest for some other dish
Put the saffron threads into a cup of warm/hot water in the measuring jug
Put some oil in the bottom of a saucepan - just enough to cover the bottom
Turn the burner/stove on and put the saucepan on it
Let the oil heat up, then toss in the crushed or cut up garlic and the celeriac and parsnips. Let the celeriac and parsnip get a little browned You will need to stir them around a bit to stop them burning.
Add the saffron and water to the saucepan. Add enough additional water to just cover the vegetables
Add pepper and salt and stock cube to the saucepan
Bring the vegetables and water to a boil and turn the heat down to a simmer. Let the vegetables cook till they are quite soft.
Put the vegetables and the water they are cooked in into a blender a little at a time and blend till its pureed.
Put the mixture back in the pan. Check how thick it is and add water to thin it to a nice soupy consistency
Heat well, pour into soup plates and put a spoonful of cream or yoghurt on top
Finally sprinkle some of the sliced leek on top of each serving of soup.