Preheat oven to 350 degrees F. Lightly spray a loaf pan with cooking spray and dust with flour. You can also line the pan with Parchment paper to make it easier to remove the cake later.
In a medium sized bowl, beat the butter and sugar until it is fluffy. Add the eggs, one at a time, mixing well after each is added.
Add the lemon zest and vanilla and beat until mixed well.
In a small bowl, whisk the flour, salt, baking soda and poppy seeds.
Alternating ingredients, add the flour mixture and the buttermilk to the butter mixture. Start and end with the flour mixture.
Pour the batter into the loaf pan and bake for 1 hour or until a toothpick inserted into the middle comes out clean. Let cool for 10 minutes.
To make the glaze, whisk the powdered sugar and lemon juice until well blended and all sugar is dissolved.
Place a cooling rack on top of a baking sheet or wax paper.
Remove cake from pan, place on the cooling rack and poke a few small holes in the top of the cake.
Brush the glaze on top, allow it to soak in and repeat.
Let cake cool completely and enjoy.