01 - Preheat oven to 350°F. Grease and flour a 10–12 cup bundt pan, ensuring all crevices are coated to prevent sticking.
02 - In a medium bowl, whisk together flour, poppy seeds, baking powder, baking soda, and salt until thoroughly blended. Set aside.
03 - In a large bowl, beat softened butter and granulated sugar with an electric mixer on medium-high speed until light and fluffy, approximately 3–5 minutes.
04 - Add eggs one at a time, beating well after each addition until fully incorporated. Mix in lemon zest, lemon juice, and vanilla extract until combined.
05 - Alternately add flour mixture and sour cream mixture to butter mixture in three additions, beginning and ending with flour. Mix gently until just incorporated, taking care not to overmix.
06 - Transfer batter evenly into prepared bundt pan. Use a spatula to smooth the top surface.
07 - Bake for 45–50 minutes, or until a wooden toothpick inserted into the center comes out clean or with just a few moist crumbs.
08 - Allow cake to rest in pan for 15 minutes before carefully inverting onto a wire rack. Cool completely before applying icing.
09 - Whisk together sifted powdered sugar, lemon juice, and lemon zest until smooth and pourable. Adjust consistency with additional lemon juice if necessary.
10 - Drizzle icing evenly over the completely cooled cake. Allow icing to set for 15–20 minutes before slicing and serving.