Preheat the oven to 180C/350F. Grease a 23x33cm (9x13 in) baking tray or line with baking paper.
In a large bowl, cream the butter and sugar together with an electric mixer until light and fluffy. Add the eggs one at a time, beating each one in well, then mix in the lemon zest and juice. The batter might ‘split’ slightly, but it will come together when the flour is added.
Sift in the flour and baking powder and gently stir to combine.
Pour the mixture into the prepared baking pan and spread it out evenly.
Bake for 20-25 minutes or until a skewer inserted in the centre comes out clean. Allow to cool for 5 minutes.
Meanwhile, mix the lemon juice and sugar and then drizzle over the top of the warm cake. Allow to cool completely, sprinkle with the lemon zest then cut into squares and serve.
The batter might ‘split’ slightly when the lemon is added to the wet mixture, but it will come together when the flour is added.
Be sure to add the drizzle while the cake is still warm - then the juice will soak into the cake and the sugar will form a lovely crust