3.Beat egg whites and cream of tartar in small bowl with electric mixer until firm peaks form.
4.Meanwhile, sift flour six times.
5.Combine flour, sugar, jelly crystals, the water, oil and egg yolks in large bowl, whisk until smooth. Fold in egg white mixture, in two batches.
6.Spread mixture into ungreased 25cm (10-inch) tube pan, smooth surface. Bake about 50 minutes.
7.Place a piece of baking paper cut larger than the pan on the bench, turn pan upside down onto bench over baking paper. Do not move or bump the pan while the cake is cooling. The cake will drop from the pan when cold.
8.Make raspberry icing. Push one-third of the raspberries through a fine sieve into small heatproof bowl, discard seeds. Reserve remaining raspberries to decorate cake. Sift icing sugar into same bowl, stir in butter and enough of the water to make a thick paste. Place bowl over small saucepan of simmering water, stir until icing is spreadable.
9.Beat cream and sifted icing sugar in small bowl with electric mixer until soft peaks form.
10.Split cake in half, place one layer on serving plate, cut-side up, spread with cream, top with remaining cake layer. Drizzle cake with icing, decorate with reserved raspberries.
It’s important to not grease the tube pan, the cake mixture needs to cling to the pan as it rises during the baking process. Tube pans are large smooth-sided ring pans with small “feet” to support the inverted pan while the cake cools. If the cake doesn’t drop from the pan when it becomes cold, gently ease it away from the side and/or base using the blade of a flexible metal spatula.