01 - Preheat oven to 350°F. Grease a 9x5-inch loaf pan and line with parchment paper.
02 - In a medium bowl, whisk together flour, poppy seeds, baking powder, baking soda, and salt. Set aside.
03 - In a large bowl, cream together butter and sugar until light and fluffy, approximately 2 to 3 minutes.
04 - Beat in eggs one at a time, mixing well after each addition.
05 - Stir in sour cream, milk, lemon zest, lemon juice, and vanilla extract until combined.
06 - Gradually add dry ingredients to wet mixture, mixing just until incorporated. Avoid overmixing.
07 - Transfer batter to prepared loaf pan and smooth the top surface.
08 - Bake for 50 to 55 minutes, or until a toothpick inserted into the center comes out clean.
09 - Let loaf cool in pan for 10 minutes, then transfer to wire rack to cool completely.
10 - Whisk together powdered sugar and lemon juice until smooth and pourable. Drizzle over cooled loaf. Sprinkle with lemon zest if desired and let set before slicing.