Preparation

• 1
  Line a baking tin [I used one that was 22cm square] with baking parchment, leaving some standing up above the edges of the tin.
• 2
  Place the condensed milk and the butter, cut into small pieces, together in a saucepan. Heat them gently, stirring them well together, for about 5 minutes, then turn off the heat.
• 3
  Break the biscuits into a food processor and pulse several times to turn them into crumbs. Alternatively, crush in a plastic bag with a rolling pin.
• 4
  Place the crushed biscuits, oats and desiccated coconut in a large bowl and mix together. [If you don’t have oaty biscuits, digestives will do just as well.] Finely grate the zest of the lemon and stir it into the dry ingredients. Stir the butter and condensed milk mixture into the bowl, making sure everything is thoroughly combined. Finally, stir in the juice of half a lemon.
• 5
  Spoon the mixture into the tin then press it in so that it is evenly spread. Leave it in the fridge for 2 hours to chill.
• 6
  To make the icing, cut the butter into small pieces and place in a large bowl with the sugar and the juice of half a lemon. Beat together with a wooden spoon to begin with, then beat with an electric whisk
• 7
  it will take a while to make sure it is really well mixed and completely smooth.
• 8
  Use the baking parchment to lift the chilled oat, biscuit and coconut mixture out of the tin, then spread the icing evenly on the top.
• 9
  In a small bowl, mix three tablespoons of desiccated coconut with the very finely grated zest of the lemon. Sprinkle it all over the icing. Leave to chill for at least 30 minutes before cutting into slices.