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 softened butter and granulated sugar in a large bowl until light and fluffy, approximately 3 minutes.
04 - Add eggs one at a time, mixing thoroughly after each addition. Blend in lemon zest, lemon juice, and vanilla extract.
05 - Gradually incorporate dry ingredients into wet mixture in three additions, alternating with milk. Begin and end with dry ingredients. Mix until just combined, avoiding overmixing.
06 - Pour batter into prepared pan and smooth the surface evenly.
07 - Bake for 45-50 minutes until a toothpick inserted in the center emerges clean.
08 - Let cake rest in pan for 15 minutes, then invert onto wire rack to cool completely.
09 - Whisk powdered sugar with sufficient lemon juice to achieve thick, pourable consistency. Drizzle over completely cooled cake before serving.