Preheat & Prep:
Preheat oven to 350°F. Set aside an ungreased 9-inch tube pan.

Sift Dry Ingredients:
Sift cake flour 4–5 times into a bowl. Add ¾ cup sugar and rainbow sprinkles. Mix with a fork to combine.

Make Meringue:
In a stand mixer, beat 12 egg whites with cream of tartar, vanilla, and salt on medium speed until frothy. Gradually add remaining ¾ cup sugar, 1 tablespoon at a time, beating to stiff, glossy peaks.

Fold in Dry Ingredients:
Gently fold flour mixture into meringue in 3 parts, being careful not to deflate. Spoon batter into tube pan and smooth the top. Tap gently to release air bubbles.

Bake & Cool:
Bake 45–50 minutes or until a skewer comes out clean. Immediately invert pan to cool upside down. Once fully cooled, run a thin knife around the edges to release.

Make Frosting:
Whisk 6 egg whites and 1¼ cups sugar in the stand mixer bowl. Place over simmering water (do not touch bowl to water), whisking until sugar dissolves and mixture is hot. Transfer to mixer and beat on medium-high until cool, glossy, and doubled in volume. Beat in vanilla and salt.

Frost & Finish:
Frost the cooled cake with marshmallow frosting, creating swoops and peaks. Lightly torch the frosting with a kitchen torch or place under a broiler until golden. Garnish with extra sprinkles.