01 - Preheat oven to 350°F. Thoroughly grease and flour a 10-cup Bundt pan, ensuring all crevices are coated.
02 - Whisk together flour, poppy seeds, baking powder, baking soda, and salt in a medium bowl. Set aside.
03 - Using a mixer, cream softened butter and granulated sugar until pale and fluffy, about 3 to 4 minutes.
04 - Add eggs one at a time, beating well after each. Stir in lemon zest, fresh lemon juice, and vanilla extract.
05 - Alternately add flour mixture and sour cream to wet ingredients, beginning and ending with flour mixture. Mix just until combined without overmixing.
06 - Pour batter evenly into prepared pan and smooth the surface. Bake for 40 to 45 minutes, or until a toothpick inserted in the center comes out clean.
07 - Allow the cake to cool in the pan for 15 minutes, then invert onto a wire rack to cool completely.
08 - Whisk powdered sugar with 2 tablespoons fresh lemon juice, adding more juice as needed for a pourable consistency. Drizzle the glaze over the cooled cake.
09 - Let the glaze set for 15 minutes before slicing and serving.