01 - Preheat oven to 350°F. Grease and flour a 10-cup bundt pan thoroughly, ensuring all crevices are coated to prevent sticking.
02 - In a medium bowl, whisk together flour, baking powder, baking soda, salt, and poppy seeds until evenly distributed. Set aside.
03 - In a large bowl, beat butter, sugar, and lemon zest until light and fluffy, approximately 3 minutes.
04 - Add eggs one at a time, beating well after each addition. Mix in vanilla extract until fully incorporated.
05 - In a measuring cup, combine milk and lemon juice. Let stand for 1 minute to slightly curdle the milk.
06 - With mixer on low speed, alternately add the flour mixture and milk mixture to the butter mixture, beginning and ending with the flour. Mix until just combined; do not overmix.
07 - Pour batter into prepared bundt pan and smooth the top. Bake for 45–55 minutes, or until a toothpick inserted in the center comes out clean.
08 - Cool in pan for 15 minutes, then carefully invert onto a wire rack to cool completely before icing.
09 - Whisk powdered sugar with 2 tablespoons lemon juice. Add additional lemon juice as needed to reach a thick but pourable consistency.
10 - Drizzle icing over cooled cake and sprinkle with lemon zest if desired. Allow icing to set for 15–20 minutes before slicing.