Preheat the oven to 180C/360F. Line and grease a 20cm x 30cm rectangular baking tray. In a large bowl place the wet ingredients and lightly whisk by hand. DO NOT over whisk/mix. Add the dry ingredients into the bowl and lightly whisk until just combined. DO NOT over whisk/mix. I like to sift my dry indredients straight into the bowl. Pour the misture into the tin and smooth the top. Place in the oven and bake for 20-25 minutes, or until cooked through. Remove from the oven and allow to cool in the tin. Do not remove until cooled completely.
Once cooled, use your ruler to mark the cake at 4cm intervals across the short edge (will make 5 pieces) and 10 cm intervals along the long edge (will make 3 pieces). Cut the cake along it's ength at these intervals to give you 15 finger pieces.
If your cake was a slightly different size just divide the short length into 5 sections and the long into 3 sections.