Preheat the oven to 350°F (175°C). Grease and flour a cake pan.

In a mixing bowl, cream together the sugar and softened butter until light and fluffy.

Add the eggs one at a time, beating well after each addition.

In another bowl, whisk together the flour, baking powder, baking soda, and salt.

Gradually add the dry ingredients to the creamed mixture, alternating with buttermilk.

Stir in the lemon zest, lemon juice, poppy seeds, and vanilla extract until just combined.

Pour the batter into the prepared cake pan and smooth the top.

Bake for 25-30 minutes or until a toothpick inserted into the center comes out clean.

Allow the cake to cool in the pan for 10 minutes before transferring to a wire rack to cool completely.

In a small bowl, whisk together the powdered sugar and lemon juice until smooth.

Drizzle the glaze over the cooled cake before serving.