Preheat oven to 175C.
Grease and dust a 7 1/2” * 3 1/2” loaf tin.
Beat together butter, sugar, vanilla and lemon zest for 5 minutes until creamy.
Add one egg at a time and beat until incorporated.
Add poppy seeds and beat until well combined.
Sift together flour and baking powder in a bowl.
Add the flour in the butter mixture and fold in with a spatula.
Transfer dough to the prepared tin and bake in the preheated oven for 45-50 minutes or until a cake tester inserted comes out clean.
Mix together lemon juice and icing sugar.
Once the loaf is out of oven, brush the top with the juice.
After 10 minutes, remove the loaf from pan, and brush all the sides with the juice.
Once the loaf is cool, wrap in cling film and let it undisturbed for 24 hours.
Slice it and enjoy with a cup of tea.
