Leave butter at room temperature until soft.
In a bowl, combine the butter and sugar and mix well until creamy.
Add the eggs one at a time, mixing well after each addition.
Sift in cake flour and baking powder, then gently fold together.
Add lemon juice and lemon zest, and mix the batter evenly.
Pour the batter into a pound cake mold.
Bake in a preheated oven at 170°C for 35-40 minutes.
Let it cool completely before serving.