01 - Preheat the oven to 350°F. Thoroughly grease and flour a 10- to 12-cup bundt pan.
02 - In a medium bowl, whisk together flour, baking powder, baking soda, salt, and poppy seeds. Set aside.
03 - Using an electric mixer on medium speed, cream the butter and granulated sugar until light and fluffy, about 3 to 4 minutes.
04 - Add eggs one at a time, beating thoroughly after each addition. Mix in lemon zest and vanilla extract.
05 - In a small bowl, blend together buttermilk and fresh lemon juice.
06 - On low mixer speed, alternately add flour mixture and buttermilk mixture to the butter mixture in three additions, starting and ending with the flour mixture. Mix just until combined to avoid overmixing.
07 - Pour batter evenly into the prepared bundt pan and smooth the surface.
08 - Bake for 40 to 45 minutes or until a toothpick inserted into the center comes out clean.
09 - Allow the cake to cool in the pan for 15 minutes, then invert onto a wire rack to cool completely.
10 - Whisk together powdered sugar, lemon juice, and lemon zest until smooth and pourable; add additional lemon juice if necessary to achieve desired consistency.
11 - Once fully cooled, drizzle glaze evenly over the cake surface. Let the glaze set before serving.