Preheat oven to 350 degrees. Grease, flour and line bottom of two 8 1/2 x 4/1/4 x 2 1/2 inch loaf pans in parchment paper.
Cream butter and 2 cups sugar in bowl of electric mixer with paddle attachment for 5 minutes or until light and fluffy. With mixer on medium speed, add eggs one at a time, and lemon zest.
Sift together flour, baking powder, baking soda, and salt in a bowl. In another bowl, combine 1/4 cup lemon juice, buttermilk and vanilla. Add flour/buttermilk mixtures alternately to the batter, beginning and ending with the flour. Divide the batter evenly between pans, smooth tops and bake 45 minutes to 1 hour until done.
Combine 1/2 cup granulated sugar with 1/2 cup lemon juice in a saucepan, cook low until sugar dissolves.
When cakes are done, cool 10 minutes. Invert them on a rack and set over a tray. Spoon syrup over cakes.
For the Glaze: combine confectioners' sugar and lemon juice in a bowl; mix with wire whisk until smooth. Pour over the tops of the cakes and allow glaze to drizzle down the sides.