Pour the evaporated milk into a metal bowl; place in the freezer until ice crystals form. Spray a 23cm springform tin with cooking spray.
Meanwhile, purée 1 cup of the raspberries in a blender or food processor, then strain through a sieve into a small saucepan. Add 1/4 cup of the sugar and the cornflour mixture. Bring to a simmer, stirring, and cook for 1 minute or until thickened. Put aside to cool slightly.
Place the gelatine in a small bowl and sprinkle on 1/3 cup cold water to soften. Place the bowl over a pan of simmering water and stir to dissolve the gelatine. Combine the cream cheese, cottage cheese, sour cream, lemon zest, lemon juice and the remaining sugar in a food processor and process until smooth. Add the dissolved gelatine and process again until smooth. Scrape into a large bowl and refrigerate until the mixture begins to mound.
Whip the partially frozen evaporated milk with an electric mixer until soft peaks form. Fold half of the raspberry sauce into the cheese mixture, then fold in the whipped milk. Fold in the remaining raspberries. Scrape the mixture into the prepared springform tin. Dollop the remaining raspberry sauce on top and swirl with a knife. Chill for 3 to 4 hours or until set. Remove the sides of the tin and serve the cheesecake cut into slices.