Place butter, syrup, sugar and cocoa in saucepan and melt over low heat. Add cornflakes, tossing until well coated. Press over base of greased loose-bottomed 7- to 8-inch (17.5 to 20 cm) round cake tin. Cool.
Cream cheese until smooth. Gradually add lemon peel, juice, sugar and egg yolks. Soften gelatine in 2 tablespoons cold water for a few minutes. Add rest of water. Pour into saucepan. Melt over low heat. Cool. Fold into cheese mixture.
Whisk egg whites until stiff. Carefully fold into cheese mixture. Pour over base, chill until set.