Heat the oven to 180C/350F/gas mark 4. Grease an approx. 22x11cm loaf tin and line with greaseproof paper.
Cream together the butter and sugar until light and fluffy, beat in the eggs one at a time, whisking well after each addition, then beat in the lemon zest. Sift in the flour, salt and ground ginger and fold in gently, then fold in the lemon juice and chopped stem ginger. Scrape the mixture into the prepared loaf tin and bake for about 45 minutes until a skewer inserted into the centre comes out clean.
While the cake is cooking prepare the topping. Rub the lemon zest and granulated sugar together in a small bowl and set aside. Put the lemon juice, stem ginger syrup and icing sugar into a small saucepan and heat gently until the sugar has dissolved.
As soon as the cake comes out of the oven, poke holes all over the top with a skewer, sprinkle over the sugar and zest mixture, then pour over the syrup, try and make sure that the whole cake gets an even dousing. Leave the cake in it's tin until it is completely cold - it is delicate while warm and may crumble.
Adapted from How To Be A Domestic Goddess By Nigella Lawson