01 - Preheat oven to 350°F. Thoroughly grease and flour a 10-12 cup bundt pan, ensuring all crevices are coated for easy release.
02 - In a medium bowl, whisk together flour, poppy seeds, baking powder, baking soda, and salt until well blended. Set aside.
03 - Using an electric mixer on medium-high speed, beat softened butter and granulated sugar until pale and fluffy, approximately 3-5 minutes.
04 - Add eggs one at a time, beating thoroughly after each addition. Blend in lemon zest, lemon juice, and vanilla extract until combined.
05 - Mix in flour mixture in three additions, alternating with sour cream and milk. Begin and end with flour mixture, mixing just until incorporated. Avoid overmixing to prevent tough texture.
06 - Pour batter evenly into prepared bundt pan, smoothing top. Bake for 45-50 minutes until toothpick inserted into center emerges clean.
07 - Allow cake to cool in pan for 15 minutes. Carefully invert onto wire rack and cool completely before icing.
08 - Whisk together sifted powdered sugar, lemon juice, and lemon zest until smooth and pourable. Adjust consistency with additional lemon juice if needed.
09 - Drizzle icing evenly over completely cooled cake. Let icing set for 15-20 minutes before slicing and serving.