Preheat the oven to 350°F
Grease and flour two 8 1/2 x 4 inch loaf pans
Zest the lemons, set aside 2 TBSP zest for the bread
Then juice them, set aside 1/4 cup of juice for the cake, and 1/4 cup of juice for the icing
Cream the butter and sugar together on medium speed until light and fluffy
Add the eggs one at a time mixing briefly after each addition
Mix in the lemon zest
In a separate bowl combine the buttermilk, lemon juice, and vanilla
In another bowl sift together the flour baking powder, baking soda, and salt
With the mixer on low speed add the buttermilk mixture and flour mixture alternately to the butter mixture
Mix just until combined
Divide the batter evenly between the prepared pans
Bake on the center rack for 45 to 60 minutes or until a toothpick inserted in the center comes out clean
Cool in the pans for 10 minutes
Remove from pans and cool completely on a wire rack