Preheat oven to 350°F / 175°C Grease and line a 9x5-inch / 23 x 13 cm loaf pan.
In a bowl combine the flour, baking powder, lemon zest, and salt and set aside.
In another bowl, beat the butter and sugar until creamy and add the eggs, one at a time, beating well after each addition. Add in the vanilla extract and lemon juice and beat well.
In this bowl, add the flour and buttermilk alternately. That is add in ½ the flour mixture and mix until just combined. Pour in half the buttermilk and mix until just combined. Repeat with the other half of the flour mixture ending with the last half of the buttermilk. Mix until just incorporated. Do not overmix.
Pour the batter into a greased and lined loaf pan and bake at 320°F /160°C for about 35 to 40 minutes or until a skewer inserted comes out clean. Remember that this is only a guide as oven temperatures vary, so it might bake a little faster or slower depending on your oven.
After it has baked, remove it from the oven and leave in the pan for 10 minutes. Remove from the pan and brush with a lemon juice and powdered sugar syrup. Allow to cool completely before adding the glaze.