Preheat oven to 350ºF (175ºC) and butter and flour a loaf tin/pan and set aside.
Sift the flour, baking powder and salt into a bowl and set aside.
Cream room temperature butter and sugar in mixer, scraping down the sides once or twice.
Add one egg, and mix well, then add about 2 tbsp of flour until blended. Continue with the rest of the eggs, and a little flour, scraping the sides of the bowl from time to time.
Now add the vanilla, lemon juice, lemon rind and lemon oil, and mix well.
Remove bowl from mixer and gently fold in the remaining flour with a spatula. Place cake batter into prepared loaf pan and put into preheated oven for 15 minutes. Then lower the temperature to 325ºF (150ºC) and continue to bake for another 40 to 45 minutes, or until tester inserted into the center comes out clean.
Let cool for 15 minutes, then remove from pan and place on rack to cool completely. When cool, prepare the icing, if desired.
Just mix the confectioner’s sugar and lemon and water until smooth. Spread or drizzle over cooled cake, letting it drip down the sides.
Allow the icing to dry/set before cutting the cake with a serrated knife.