Preheat the oven to 325° F / 160° C / 140° Fan / Gas 3. Grease & line a loaf tin. Cream together the butter and sugar until pale and fluffy. Add the lemon curd & zest and cream together.
Slowly add the beaten eggs and beat together until lump free. Add the poppy seeds and mix well.
Finally add the flour and mix thoroughly until smooth. Carefully spoon the batter into the tin and bake for 50-60 minutes or until a skewer comes out clean.
Whilst the cake is in the oven, mix the caster sugar and lemon juice for the crunchy topping together in a small jug or cup and put to one side.
When the cake is baked, remove it from the tin and place face up on a wire rack, with a large plate or tray underneath it.
Then straight away whilst the cake is still hot spoon the lemon juice and sugar mixture onto the top of the cake so it runs down the sides. Try and get it as even as possible so the entire top of the cake is covered. Then leave until completely cool before slicing and serving.