For the base: Mix all the ingredients in a bowl and knead into a dough.
Line the baking tin with baking paper and press the dough into the tin. Bake for approx. 18-20 minutes until golden brown.
For the mixture: Mix together the eggs, flour, sugar and the fruit juice alternately while stirring. Finally, add the grapefruit zest. The mixture is very runny, but it will firm up as it bakes, so don’t panic.
Once the base is baked, pour the mixture directly on top and place in the oven for a further 20 minutes.
Then let the bars cool completely and freeze for about 1-2 hours. Cut into pieces and eat. If you have any left over, keep them in the fridge.