01 - Preheat oven to 350°F. Grease a 9x5 inch loaf pan and line with parchment paper.
02 - Whisk together flour, poppy seeds, baking powder, baking soda, and salt in a medium bowl.
03 - Beat butter and sugar in a large bowl until light and fluffy, about 2–3 minutes.
04 - Add eggs one at a time, beating well after each addition.
05 - Mix in lemon zest, lemon juice, vanilla extract, milk, and sour cream until combined.
06 - Gradually add dry ingredients to wet mixture, mixing until just combined. Do not overmix.
07 - Pour batter into prepared loaf pan and smooth the top.
08 - Bake for 45–55 minutes, until a toothpick inserted into the center comes out clean.
09 - Let cool in pan for 10 minutes, then transfer to wire rack to cool completely.
10 - Whisk powdered sugar and lemon juice until smooth. Drizzle over cooled loaf before serving.