In a large bowl, mix the butter, sugar and lemon zest until as light and fluffy as you can get it (it won’t always be as light as regular white sugar but you can get it pretty fluffy!)
Beat in the two eggs.
Fold in the flour and the milk.
Pour into a small loaf cake tin, about 16cm x 11cm (roughtly the 1lb size, it’s only a little cake) and bake in the middle rack of the oven, checking after 30 - 40 minutes. It may need a little more, depending on how hot your oven is. Mine runs fairly cool.
Remove cake from the oven when it is firm to the touch and a skewer inserted in the centre comes out clean. leave in the tin.
In a small saucepan, heat the lemon juice and 50g sugar until sugar is dissolved. pour gently over the cake, allowing it to soak in. It can take some time! Some people poke holes in with a skewer, all over the top, to allow the syrup to go further down into the cake, but it’s ok if you don’t.