01 - Preheat oven to 350°F. Grease and flour a 9-inch bundt or loaf pan.
02 - Whisk together flour, poppy seeds, baking powder, baking soda, and salt in a medium bowl.
03 - Beat butter and sugar in a large bowl until light and fluffy, approximately 3 to 4 minutes.
04 - Incorporate eggs one at a time into the butter mixture, beating well after each addition. Mix in lemon zest and lemon juice.
05 - Add the flour mixture to the wet ingredients in three additions, alternating with buttermilk, beginning and ending with the flour mixture. Stir in vanilla extract.
06 - Pour batter into the prepared pan and smooth the surface. Bake for 40 to 50 minutes until a toothpick inserted into the center comes out clean.
07 - Allow the cake to cool in the pan for 15 minutes, then turn out onto a wire rack and cool completely.
08 - Whisk powdered sugar with lemon juice in a small bowl until smooth and pourable. Drizzle over the cooled cake and let set before slicing.