Pre-heat oven to at least 220 C or 430F
Mix flour, yeast, sugar and salt in a big bowl. Using your fingertips rub in margarine until it looks like fine crumbs.
Mix in the water with a cutlery knife until it's a ball of dough.
Tip mix onto lightly floured surface and knead for 10 minutes (or use a dough hook in an electric mixer).
Flour the dough and leave to rise in the clean bowl that's also been well dusted with flour. Cover with a tea towel and leave somewhere draught free and warm until doubled in size - this could take up to an hour.
If you want you can cover bowl with a plastic bag and leave in the fridge overnight and it will still prove but more slowly (and apparently the flavour will be better).
Turn out onto floured surface.
I stretch, fold and turn the dough a bit like an envelope - pulling one side out and into the middle and then turn and do the same again three or four times.
Then I gently shape into a round ball and dust well with flour (see the link to the video in the above article).
And put seam down, back into the bowl which has been floured again and cover.
Leave for 30 minutes.
Meanwhile heat a dutch oven with the lid on in the pre-heated oven for 30 minutes.
This is a heavy cast iron enamel pot with a lid - like a Le Creuset at least 12cm deep (4 1/2 inches) and 19 cm in diameter (mine is 19cm at the bottom and slopes out to 24cm at the top).
Remove from oven and take lid off and gently slip the proved dough seam side UP into it.
Replace lid and put back into oven for 30 minutes.
Remove from oven and lift lid.
Gently turn out without burning yourself and cool on a rack. Slice and eat!