Preheat your oven to 350°F (175°C) and prepare a 9-inch ungreased tube pan.

Sift the cake flour 4-5 times into a bowl, then combine with 3/4 cup sugar and rainbow sprinkles.

In a separate bowl, beat egg whites, cream of tartar, vanilla, and salt until frothy. Gradually add remaining sugar until stiff peaks form.

Gently fold the flour mixture into the meringue until just combined.

Pour the batter into the tube pan, smoothing the top gently.

Bake for 45-50 minutes until risen and a toothpick comes out clean. The top should be golden.

Once baked, cool the cake upside down on a cooling rack for about 1 hour.

Prepare the frosting by whipping egg whites and sugar over simmering water until stiff peaks form, then add vanilla.

Spread the meringue frosting over the cooled cake and optionally toast with a torch.