Preheat the oven to 350F degrees. Butter a 6-cup loaf pan and line it with parchment paper. In a medium bowl, combine the flour, baking powder, and salt.
In a mixer fitted with a whisk attachment, cream the butter. Add 1 cup of the sugar and mix. With the mixer running at low speed, add the eggs one at a time. Add the vanilla.
Working in alternating batches, and mixing after each addition, add the dry ingredients and 1/4 cup of the lemon juice and zest to the butter mixture. Mix until just smooth.
Pour into the prepared pan and bake until raised in the center and a tester inserted into the center comes out dry and almost clean, 65 to 75 minutes.
When the cake is done, let cool in the pan 15 minutes (it will still be warm). Run a knife around the sides of the pan. Set a wire rack on a sheet pan with sides.
When the cake is cool, carefully(large spatula) transfer to a serving platter.
Combine the confectioners' sugar, lemon juice, lemon zest and melted butter in a medium bowl, mixing with a fork until smooth. Add more confectioners' sugar or lemon juice as necessary to make a thick but pourable glaze(like syrup). Spoon the glaze over the top of the cake.