01 - Preheat oven to 350°F. Grease and flour a 12-cup bundt pan thoroughly, ensuring all crevices are coated to prevent sticking.
02 - Whisk together flour, poppy seeds, baking powder, baking soda, and salt in a medium bowl until uniformly combined.
03 - Beat butter and sugar with electric mixer on medium-high speed until light and fluffy, approximately 3-4 minutes.
04 - Add eggs one at a time, mixing thoroughly after each addition. Incorporate lemon zest, lemon juice, and vanilla extract until blended.
05 - Add dry ingredients in three alternating portions with buttermilk, beginning and ending with dry ingredients. Mix just until combined; avoid overmixing.
06 - Spoon batter evenly into prepared bundt pan, smoothing top with spatula to ensure even distribution.
07 - Bake for 38-42 minutes until toothpick inserted into center emerges clean.
08 - Let cake rest in pan for 15 minutes, then invert onto wire rack to cool completely before glazing.
09 - Whisk powdered sugar and lemon juice until smooth and pourable. Drizzle over cooled cake and allow to set before slicing.