Chiffon Cake

1. Preheat oven to 320 F and prepare a baking pan fit with a parchment paper.
2. Whisk together the milk, oil, 2 1/3 tbsp sugar, and vanilla in a small bowl and set aside.
3. Sift together the flour and salt into a separate large bowl, whisk to combine, then add the wet ingredients mixture. Whisk just until combined.
4. Add the egg whites and cream of tartar into the bowl of stand mixer fitted with the whisk attachment. Whisk on low speed until frothy, then increase the speed to medium and whisk for 3-5 minutes until egg whites form soft peaks. Add the second portion (1/3 cup) of granulated sugar in 3 steps, then increase the speed of a mixer to highest and whip for 3-5 minutes until stiff peaks have formed.
5. Carefully add the meringue to the flour mixture in 3 steps, gently folding in with silicone spatula.
6. Separate this chiffon cake batter into 6 bowls, leaving one white/uncolored and tint the other 5 into your desired colors (pink, yellow, green, blue, purple).
7. Fill the piping bags with the batter. Using the uncolored/white batter, pipe the clouds onto the parchment paper. Freeze for 5 minutes.
8. Pipe the colored rainbow batter, starting from the left corner of the parchment/pan in desired order, making sure to lightly tap the pan on the counter after piping each color to remove any air pockets.
9. Bake on middle rack at 320F for 12-14 minutes until toothpick comes out clean and the cake springs back when touched in the center.
10. Allow to cool in the pan for 5 minutes, then place the cooling rack over the baking pan and flip the cake onto the cooling rack; gently peel-off the parchment paper. Set aside to cool completely while you prepare the stabilized chantilly cream.

Stabilized Chantilly Cream

1. Combine the cold water and gelatin in a small bowl and set aside to "bloom" for at least 5 minutes.
2. Melt the bloomed gelatin in the microwave for 5-10 seconds until fully melted, set aside to cool.
3. Add the heavy cream, sugar and vanilla to the bowl of stand mixer fitted with the whisk attachment and whip on medium speed for 2-3 minutes to soft peaks.
4. Pour the cooled melted gelatin right on the cream in thin steady stream while the mixer is still whipping on medium speed. Increase the speed to highest and continue mixing until the cream reaches stiff peaks; do not over whip.

Assembly

1. Flip the cooled cake from cooling rack onto a parchment paper.
2. Spread the chantilly cream onto the rainbow chiffon cake, placing a bit thicker layer on the shorter side that will be rolled first. Refrigerate the remaining cream for later use.
3. Gently roll up the cake from the short edge, using the parchment paper to help you push the cake onto itself.
4. Transfer the rolled cake onto a large piece of kitchen plastic, wrap and refrigerate for at least 2 hours before decorating and serving.
5. Once cake have set and cooled, add the remaining chantilly cream onto the piping bag fitted with 1M piping tip; decorate the top of the cake with piped rosettes, whole and crushed mini Cadburry eggs.