Preheat oven to 175 C (350 F) and grease and flour a 20cm x 30cm (9 x 13) pan.
To make base
In a medium bowl, whisk together flour and icing sugar. Cut the butter into small cubes and using your finger tips, rub into the flour until combined and crumbly (alternatively you could use a food processor) 3. Press mixture into bottom of pan and smooth with hands. Bake for 20 minutes or until just golden brown.
To make topping
While the base is baking, prepare topping – In a larger bowl, sift sugar, flour, and baking powder together and whisk to combine.
Add slightly beaten eggs and lemon juice and mix well. Pour on top of warm baked base and bake for 20-25 minutes.
When cool, dust with icing sugar and cut into desired sized bars (either 12 large bars or 24 smaller bars).
Notes
Bars are best stored in an airtight container in the fridge and are best before 7-9 days.