Preheat oven to 180 C / 350 F. Arrange an oven rack in the middle of the oven. Grease and line a 9 x 5 - inch loaf tin with baking paper.
Place lemon zest and granulated (caster) sugar in a large bowl. Using your finges, rub zest into sugar for about 2-3 minutes or until fragrant.
Add eggs. Whisk until sugar is dissolved completely.
Add oil, milk, sour cream, lemon juice and lemon extract (if using). Whisk until just combined.
Sift in flour and baking powder. Fold in gently.
Pour batter into loaf tin. Bake for 45-50 minutes or until a skewer inserted into the center of the cake comes out clean.
Remove from oven. Turn on to a wire rack. Let cool for about 30 minutes before drizzling with lemon glaze.
To make the lemon glaze, combine together icing or confectioner’s sugar, lemon juice and milk.
Pour glaze over the cake and leave to cool completely.