Preheat the oven to 350 degrees F. Grease and flour two 5x8 inch loaf pans.
Use an electric mixer to cream the butter with 2 cups of the granulated sugar in a large bowl. Beat 5 minutes, or until light and fluffy. With the mixer on medium speed, add the eggs one at a time, and then the lemon zest.
In a separate bowl, sift together the flour, baking powder, baking soda, and salt. In another bowl, combine ¼ cup lemon juice, buttermilk and vanilla. Add the flour and buttermilk mixtures alternately to the batter, beginning and ending with the flour.
Divide the batter evenly between the two loaf pans. Bake 50 to 60 minutes, or until a toothpick inserted into the center comes out clean.
Combine ½ cup granulated sugar with ½ cup lemon juice in a small saucepan and cook over low heat until sugar dissolves.
When the cakes are finished, allow them to cool for 10 minutes. Remove the cakes from the pans and set them on a rack placed over wax paper. Poke holes throughout the top of the cake with a skewer. Spoon the lemon syrup over the cakes. Allow them to cool completely.
GLAZE
Combine the powdered sugar and the lemon juice in a bowl, mixing with a wire whisk until smooth. .
Pour over the tops of the cakes and allow the glaze to drizzle down the sides
Notes
Try greasing and "sugaring" the loaf pans, instead of flouring them. You won't get the visual of the flour stuck on the loaf, and it adds a little sweetness to the outside of the loaf.