01 - Preheat the oven to 350°F. Grease and flour a 10-12 cup Bundt pan thoroughly, tapping out excess flour.
02 - In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and poppy seeds. Set aside.
03 - In a large bowl, using an electric mixer, cream the butter and sugar together until light and fluffy, about 3 minutes.
04 - Beat in the eggs, one at a time, mixing well after each addition. Scrape down the sides of the bowl as needed.
05 - Mix in the lemon juice, lemon zest, and vanilla extract until just combined.
06 - On low speed, alternately add the flour mixture and the milk to the butter mixture in three additions, beginning and ending with the flour. Mix until just combined; do not overmix.
07 - Fold in the sour cream until the batter is smooth and even.
08 - Pour the batter evenly into the prepared Bundt pan. Smooth the top with a spatula. Bake in the center of the oven for 45-55 minutes, or until a skewer or cake tester inserted into the center comes out clean.
09 - Let the cake cool in the pan for 15 minutes, then carefully invert onto a wire rack and cool completely.
10 - Whisk together the powdered sugar, lemon juice, and lemon zest until smooth and pourable. Drizzle over the cooled cake before serving.