01 - Preheat oven to 350°F. Thoroughly grease and flour a 10-12 cup bundt pan.
02 - Whisk together flour, baking powder, baking soda, salt, and poppy seeds in a medium bowl.
03 - Beat butter and sugar on medium-high speed until light and fluffy, about 3 minutes.
04 - Add eggs one at a time, beating well after each. Mix in lemon juice, zest, and vanilla.
05 - On low speed, add flour mixture in three additions alternating with sour cream and milk, beginning and ending with flour. Mix just until combined.
06 - Spoon batter into prepared pan, smooth top. Bake 45-50 minutes until skewer comes out clean.
07 - Cool in pan 15 minutes, then invert onto wire rack to cool completely.
08 - Whisk powdered sugar, lemon juice, and zest until smooth and pourable. Adjust juice for consistency.
09 - Drizzle glaze over cooled cake. Let set before slicing.