Preheat the oven to 180 degrees Celsius (350 Fahrenheit).
To make the sponges, add the soft butter and sugar to a large mixing bowl, and use a hand mixer to cream them together until you have a smooth texture.
Add the eggs one by one, beating well after every addition.
Sift in the flour, add the baking powder, lemon zest and milk, and use a spatula to mix well to get a smooth batter.
Butter and flour 4 mini loaf tins ( mine were 13.5 x 6.5 x 3.5 cm or 5.3 x 2.6 x 1.4 inches).
Divide the batter evenly between each tin, and bake for 25 to 30 minutes, or until the sponges are well risen and golden, and a skewer inserted in the middle comes out clean.
Remove the cakes from the oven.
To make the lemon drizzle, mix the granulated sugar with the lemon juice, then pour it over the hot sponges.
Allow the cakes to cool down completely.
To make the icing, sift the icing sugar with the lemon juice, and mix well to get a smooth thick paste that is still pourable. Add more lemon juice is necessary.
Pour the icing over the cakes, and allow the icing to set before slicing.
Garnish with lemon zest (optional).