Start by making the pastry cream. Put the milk, lemon zest and vanilla in a pan and heat till almost boiling. Meanwhile, whisk the egg yolks and sugar together in a bowl for 2 minutes till light and pale in colour. Whisk in the corn flour and plain flour, and then whisk in the almost boiling milk, stirring constantly. Put this mixture back into the saucepan and bring to the boil whisking all the time. When the pastry cream has thickened, allow it to come to the boil and then remove it off the heat. Finally, stir in the butter. Pour the pastry cream into a dish, cover with cling film, and leave to cool down for an hour to set. Next, prepare the puff pastry by rolling out each piece very thin, to 30cm x 14cm in size. Place the 3 pieces of puff pastry onto greased baking trays and prick all over with a fork. Bake in the oven for about 45 minutes at 150`c, as at this temperature you will be drying out the pastry to make it crisper. Remove the cooked puff pastry from the oven and put aside to cool. When the cooked puff pastry is ready, brush 2 piece with the melted chocolate and leave till set for 10 minutes. When ready, take the first piece of puff pastry and place on a long serving dish. Spread 1/3 of the cold pastry cream on top, and place the other chocolate covered piece of puff pastry on top. Spread this with ½ the remaining cream and place the last piece of puff pastry on top. Spread on the remaining pastry cream and smooth on top with a palette knife. Finally, cover the top of the mille-feuille with the whole strawberries, side by side. Place in the fridge to chill for 30 minutes. To serve, dust the top of the mille-feuille with icing sugar. (Serves 12)