For the Cake:

1. Preheat oven to 325°F (163°C). In a food processor or blender, pulse the sugar until it's fine. Remove 1 cup and set aside; keep the rest in the processor. Add the cake flour and salt. Pulse 5-10 times until the flour/sugar/salt mix is light.
2. In a large bowl, whip egg whites and cream of tartar on medium-low until foamy (about 1 minute). Switch to medium-high and slowly add the 1 cup of sugar that was set aside. Whip until soft peaks form, about 5-6 minutes. Add the vanilla extract and beat until just mixed in.
3. In multiple additions, slowly sift the flour mixture into the egg white mixture, gently folding with a rubber spatula to avoid a dense cake. Pour and spread batter into a very lightly greased bundt pan.
4. Bake until a toothpick comes out clean, about 40-45 minutes. Remove from the oven and cool the cake upside-down on a wire rack for about 2 hours (or let sit in fridge).
5. Once cooled, run a thin knife around the edges and gently tap until the cake releases.

For Decoration:

1. To make the frosting: In a bowl, combine softened butter, confectioner's sugar and milk. Beat until smooth and fluffy. Add 2-3 drops of food coloring to buttercream and continue to beat until well distributed. Transfer frosting into piping bag and carefully dot the circumference of the cake.
2. Top with multicolored candies. Shape stars out of yellow fondant and place on cake.

Recipe Notes: Can be cooled in the fridge; can be stored in the fridge for up to 5 days