I wondered if there should be some sugar in Nigella's Hot Cross Bun recipe?
Nigella's Hot Cross Buns (from Feast and on the Nigella website) don't contain added sugar in the dough as they contain quite a lot of dried fruit which provides sweetness. There are a lot of spices in the dough and a cardamom infused milk is used, both of which add flavour. The buns are also glazed with a sugar syrup just after they are baked.
However if you did want to add some sugar to the dough we would suggest using 1 to 2 tablespoons of caster (superfine) sugar. The sugar should be stirred into the flour at step 2, along with the yeast, spices and dried fruits. A sugary dough can burn slightly more easily so you may need to keep an eye on the buns while they are baking, and turn the oven down to 200c/400F if necessary.