01 - Preheat the oven to 350°F. Grease and flour a 10-12 cup Bundt pan thoroughly, ensuring all crevices are coated to prevent sticking.
02 - In a medium bowl, whisk together the flour, poppy seeds, baking powder, baking soda, and salt until well combined. Set aside.
03 - In a large bowl, beat the softened butter and granulated sugar with an electric mixer on medium speed until light and fluffy, approximately 3-4 minutes.
04 - Add the eggs one at a time, beating well after each addition. Mix in the lemon zest, lemon juice, and vanilla extract until fully incorporated.
05 - On low speed, alternately add the flour mixture and sour cream to the butter mixture, beginning and ending with the flour mixture. Mix until just combined; take care not to overmix.
06 - Pour the batter evenly into the prepared Bundt pan and smooth the top. Bake for 45-50 minutes, or until a toothpick inserted into the center comes out clean.
07 - Allow the cake to cool in the pan for 15 minutes, then carefully invert onto a wire rack. Let cool completely before glazing.
08 - Whisk together the powdered sugar, lemon juice, and lemon zest until smooth and pourable. Adjust consistency with additional juice if needed.
09 - Drizzle the glaze over the completely cooled cake, allowing it to cascade down the sides. Let set for 15-20 minutes before slicing and serving.