Preheat oven to 350F (177 Celsius).
Lightly grease a 9 x 5" (23 x 13cm) loaf pan with butter. Line with parchment paper long ways for easy removal of loaf after baking.
Using a rasp, grate lemon rind.
Using a hand or stand mixer, cream the butter, sugar, lemon rind and vanilla until light and fluffy (about 5 minutes).
Add the eggs 1 at a time being sure to beat well after each one. Continue beating for another 2-3 minutes after all eggs have been added.
Whisk together the flour, baking powder and salt. Add the flour mixture to the butter mixture alternatively with the buttermilk, beginning and ending with the dry ingredients. Make sure it's completely mixed without over beating.
Pour the batter into the loaf pan making sure to spread it out evenly. Bake on the center rack for 50-55 minutes or until a toothpick inserted in the center comes out clean.
Allow the cake to cool in the pan for about 15 minutes. Use the parchment paper to transfer the cake to a wire rack. Remove the parchment paper and allow the cake to fully cool.
When cake is cooled whisk together the icing sugar with enough lemon juice to make a thick glaze and spread over the cake. Allow the glaze to harden before serving.