01 - Preheat oven to 350°F. Thoroughly grease and flour a 10-cup Bundt pan.
02 - In a medium bowl, whisk flour, poppy seeds, baking powder, baking soda, and salt together. Set aside.
03 - Using an electric mixer, beat butter and sugar until light and fluffy, about 3 to 4 minutes.
04 - Incorporate eggs one at a time, blending well after each, then stir in lemon zest and vanilla extract.
05 - Blend fresh lemon juice and sour cream into the batter until combined; mixture may appear slightly curdled.
06 - Gradually fold dry ingredients into wet mixture, stirring just until incorporated to avoid overmixing.
07 - Pour batter into prepared pan, smoothing the top evenly.
08 - Bake for 45 to 50 minutes or until a toothpick inserted in the center comes out clean.
09 - Let the cake cool in the pan for 15 minutes, then invert onto a wire rack and cool completely.
10 - Whisk powdered sugar, lemon juice, and zest until smooth and pourable; drizzle over cooled cake.
11 - Allow glaze to set for 10 minutes before slicing and serving.