Preheat oven to 180C/350F.
Beat egg whites and cream of tartar in a small bowl with an electric mixer until firm peaks form.
Sift flour and baking powder six times. Combine flour, sugar, jelly crystals, the water, oil and egg yolks in a large bowl; whisk until smooth. In two batches, fold in the egg white mixture. Spoon the mixture into an ungreased 25cm (10 inch) (top measurement) tube pan and smooth the surface.
Bake the cake for about 50 minutes.
Place a piece of baking paper, cut larger than the pan, on the bench; turn pan upside down onto bench over the baking paper. Do not move or bump the pan while the cake is cooling; the cake will drop from the pan when it is cold.
To make raspberry icing, push one-third of the raspberries through a fine sieve into a small heatproof bowl; discard seeds. Reserve the remaining raspberries to decorate the cake. Sift icing sugar into the same bowl; stir in butter and enough of the water to make a thick paste. Place bowl over a small saucepan of simmering water; stir until icing is spreadable.