Preheat the oven to 350°F (175°C). Grease and flour a 9-inch cake pan.
In a bowl, whisk together flour, baking powder, baking soda, and salt.
In a separate bowl, cream together butter and sugar until fluffy.
Beat in eggs, vanilla extract, and lemon zest.
Gradually add the dry ingredients, alternating with buttermilk, mixing until just combined.
Pour the batter into the prepared pan.
In a small bowl, mix sugar and lemon zest, then sprinkle it over the batter.
Bake for 40 minutes, or until a toothpick inserted in the center comes out clean.