Preheat your oven to 350°F (175°C) and grease a loaf pan.
In a large bowl, whisk together the flour, sugar, poppy seeds, baking powder, baking soda, and salt.
In a separate bowl, cream together the softened butter and sugar until light and fluffy.
Add eggs, one at a time, beating well after each addition.
Stir in sour cream, lemon juice, lemon zest, and vanilla extract until fully combined.
Gradually mix in the dry ingredients until the batter is smooth.
Pour the batter into the prepared loaf pan and bake for 50-55 minutes, or until a toothpick inserted into the center comes out clean.
Let the loaf cool in the pan for 10 minutes before transferring to a wire rack to cool completely.
While the loaf cools, make the glaze. In a small bowl, whisk together powdered sugar, lemon juice, and lemon zest until smooth.
Drizzle the glaze over the cooled loaf and allow it to set before slicing and serving.