01 - Preheat oven to 350°F. Grease and flour a 10-cup Bundt pan or 9x5-inch loaf pan.
02 - Whisk together flour, poppy seeds, baking powder, baking soda, and salt in a medium bowl. Set aside.
03 - Beat butter and sugar in a large bowl until light and fluffy, approximately 3 minutes.
04 - Add eggs one at a time, beating well after each addition. Mix in lemon zest, lemon juice, and vanilla extract.
05 - Gradually add dry ingredients to wet mixture in three additions, alternating with milk. Begin and end with dry ingredients. Mix until just combined.
06 - Pour batter into prepared pan and smooth top. Bake for 45-50 minutes until toothpick inserted into center comes out clean.
07 - Let cake cool in pan for 15 minutes, then turn out onto wire rack to cool completely.
08 - Whisk powdered sugar with enough lemon juice to achieve thick but pourable consistency. Drizzle over cooled cake before serving.