Rainbow Swiss Roll Recipe

Swiss roll batter

1. Lightly grease a 10 x 15 inch jelly roll pan with butter. Line the pan with parchment paper, with an overhang along the short edges of the pan (to make it easy to remove the cake from the pan). Dust the exposed edges with flour. Set aside.
2. Preheat the conventional oven to 325°F / 163°C.
3. Sift the flour, cornstarch, and baking powder into a separate small bowl.
4. Add a few inches of water into a medium saucepan, and bring it to a simmer on your stove.
5. Record the weight of your empty mixing bowl. Make sure the mixing bowl can fit over the saucepan.
6. Place the eggs and yolk in the mixing bowl. Then add the vanilla, sugar and salt, and whisk to combine.
7. Place the mixing bowl on the saucepan over the simmering water (without touching the water), and whisk continuously for about 2 – 4 minutes until the egg mixture is warm to the touch or until the eggs reach a temperature of about 110 – 120°F.
8. Remove the egg mixture from the heat. Then remove the saucepan from the heat.
9. Place the mixing bowl in your stand mixer, with the whisk attachment. Whisk on high speed for about 5 – 6 minutes. The eggs should at least triple in volume.
10. To check if the egg mixture is at the right consistency, take some of the egg mixture with your whisk attachment and create some ribbons on the surface. The ribbons should remain on the surface and not immediately disappear.
11. Sift the dry ingredients evenly over the surface of the egg mixture. Make sure it's sifted evenly, so that the flour doesn't collect at one spot and sink to the bottom.
12. Using a wide spatula (or the largest spatula you own), fold the flour into the egg mixture. Rotate the bowl after every fold to make sure all the flour is well incorporated, and there are no dry spots in the batter or the bottom of the bowl. Be careful not to deflate the mixture by overmixing.

Coloring the batter

1. Weigh the mixing bowl WITH the batter. Deduct the weight of the empty bowl from this value. This is the weight of the batter. Divide this value by 6 to get the weight of each of the individual portions.
2. Evenly divide the batter (by weight) into 6 bowls. (If you don't have 6 bowls, you can do this one at a time, taking care to wash the bowl between each colored portion. But this will be more time consuming.)
3. Add a few drops of the appropriate gel food coloring into each bowl of batter. Using a small spatula, mix the food coloring into the batter. Use small circular motions to dissolve the food coloring into a small area of the batter, and then fold the batter through to mix it in uniformly.
4. Scrape the batter into uncut pastry bags, or ziploc bags. Seal the bags (with a knot), and set aside.
5. Repeat with all the colors to get the 6 colored batter portions.

Piping the batter into the pan, baking, and rolling up the cake

1. You will be piping 12 even strips of color into the cake pan, parallel to the short edge (i.e repeating the 6 color segment once for a total of 12 sections - see images in the post). You could also pipe the batter diagonally if you prefer.
2. Start with red, and then go orange, yellow, green, blue, and purple. Try to make the strips as even as possible.
3. Knock the pan on a hard surface (kitchen counter) about 3 - 4 times to remove any big bubbles trapped in the batter.
4. Bake in the preheated oven for about 12 - 15 minutes. It takes 13 minutes in my oven. The cake is done when the cake surface is springy to the touch, and the cake is starting to pull away from the sides. The cake surface should not have browned too much either.
5. Remove the pan from the oven and let it cool down slightly, for about 1 minute.
6. While the cake is still warm, gently remove the cake from the pan (using the parchment paper), and place it on your work surface.
7. Dust the surface with confectioner's sugar, and roll up the swiss roll while it's still very warm. Start at one of the short edges, and roll it up along the long edge, with the help of the parchment paper that is attached to the cake.
8. Wrap the cake with a cloth napkin / kitchen towel and allow the cake to cool down to room temperature completely. Make sure the cake is stored with the seam-side down to help seal the cake.
9. Make the filling once the cake has cooled down. (See below.)

Filling the cake

1. Once the cake is completely cooled down, gently unravel it.
2. Spread a thin layer of stabilized chantilly cream, about ½ – 1 cm (¼ – ½ inch) thick, on the surface. Leave a 1 - 1½ inch border at the second short edge that will form the seal.
3. Now roll up the cake again, but loosen the parchment paper from the cake as you go. Make sure the cake is firmly rolled up, while maintaining its shape, and the filling isn't squeezed out much. Wrap the cake well with parchment paper and/or a cloth napkin so that the cake doesn't lose its shape. You can use the parchment paper to shape the cake if the roll seems loose.
4. Make sure the cake is stored with the seam-side down, to hold its shape.
5. Refrigerate for a few hours until the cake and filling have firmed up.
6. Slice off the ends with a warm, sharp or serrated knife, so that the swiss roll cake looks neat.
7. Serve with a dusting of confectioner's sugar.

Stabilized cream chantilly (sweetened whipped cream)

1. Place the water in a small microwave-safe bowl and sprinkle the gelatin over the surface. Mix with a toothpick to saturate the gelatin. Let it sit for about 10 minutes until the gelatin has bloomed.
2. Place the chilled cream (1 cup) in a mixer bowl (preferably chilled bowl). Add the confectioner's sugar and vanilla, and whisk to mix the ingredients together. Set aside until the gelatin is ready.
3. Microwave the bloomed gelatin for just 15 – 20 seconds until the gelatin is dissolved. Do NOT let it boil. I prefer to microwave in 5 – 10 second bursts and check in between to make sure the gelatin has fully dissolved in the water (a clear liquid with no granules).
4. Stir in 1 tbsp of cream to temper the temperature of the gelatin mixture.
5. Whisk the cream on medium high – high speed using the whisk attachment in your stand mixer.
6. Pour the gelatin mix carefully, while the mixer is running, and whisk for a few seconds until the gelatin has mixed through. The gelatin mixture should be poured into the cream and NOT on the whisk, as it will solidify and form lumps then.
7. Lower the speed to medium, and whisk the cream until it starts to thicken and form soft peaks.
8. Continue to whisk the cream until it reaches stiff peaks, but is still creamy. I prefer to whisk the cream by hand after reaching soft peaks stage, so that I don’t risk curdling the cream.
9. The cream is now ready to be used.