Follow the order of these instructions as they may for one of the best cake recipes. 

1. Preheat oven oven temperature to 200c
2. Add the flour, sugar and baking powder to a large mixing bowl and mix well together. 
3. Add the melted butter to the dry ingredients along with the eggs and incorporate fully without over-mixing. You can easily do this by hand or using the paddle attachment if using a mixer.
4. Zest three lemons and add the zest to the mixture, incorporate the zest into the batter. 
5. Grease and line a 12x16" baking tray with baking paper and pour the batter into the tray. 
6. Bake in the oven for 25mins or until a skewer comes out of the centre of the cake clean. Depending on your oven, if it looks like the top of the cake is baking too quickly and the centre is not then turn the oven down to 180c to finish off. 
7. Remove the cake from the oven and lift it out of the tray and onto the wire rack. Allow to cool completely before icing. 
8. You may want to straighten the edges of the cake and flatten the top by cutting the edges and levelling off the top. Use a long, sharp bread knife to do this if you think it necessary. 
9. Add the sifted icing sugar to a bowl along with the juice of one of the lemons and begin to mix. Add a little water, a few drops at a time until the icing has been completely mixed and pourable but remains thick, not watery.
10. Starting in the centre of the cake, spread the icing across the top of the cake. Allowing it to spread to the edges but giving it a little nudge if it needs help getting there. 
11. When the icing has been applied to the top of the cake, distribute colourful sprinkles the cake sprinkles all over the top of the icing. Allow the icing to set for at least an hour before cutting into 12 square pieces.