Preheat the oven to 170C Gas Mark
3, grease and line an 7 in round cake tin.
Cream the butter and sugar
together in a bowl until light and fluffy, then beat in the lemon
Add the eggs, a little at a time,
beating well after each addition, sifting in a little of the flour,
if necessary, to prevent curdling.
Sift the flour with the baking
powder, salt and cinnamon, and lightly stir it into the creamed
mixture with the milk and lemon juice - it is most important not to
beat at this stage, just mix all the ingredients thoroughly.
Pour the mixture into the tin,
smooth the top and place the citron peel, if using, in the centre.
Bake for 90-105 minutes, until a
fine skewer inserted into the centre comes out clean.