Make the cake:

Cup of Yum
1. Preheat oven to 325°F/163°C.
2. Prepare a 9" by 13" baking sheet with parchment paper. Ready another large piece of parchment paper for later use.
3. In a medium glass bowl, combine the oil, milk, sugar, vanilla and mix together. Add in both flours and stir until combined.
4. In a clean stand mixer bowl fitted with a whisk, add in 4 egg whites and beat on low-medium speed until foamy.
5. Gradually increase the mixer speed and add in the cream of tartar. When you begin to see lots of bubbles, add in the granulated sugar gradually and continue beating until egg whites reach firm peaks.
6. Transfer 1 C of the whipped egg whites to the flour mixture and fold. Once lightened, add the remaining egg whites to the flour mixture to incorporate. Be careful not to overmix.
7. Transfer the batter to the prepared baking sheet and smooth out the top with an offset spatula. Drop the pan from a height of 1 feet to release any trapped air bubbles.
8. Bake at 325°F/163°C for 12-15 mins, or until the cake is springy and firm to the touch.
9. Remove from the oven and drop the pan from a height of 1' to prevent the cake from shrinkage.
10. Let cool on a cooling rack for about 20 minutes.

Make the cream filling:

1. In a medium glass bowl, add the heavy whipping cream, blue butterfly pea powder and powdered sugar. Whisk until firm peaks.
2. Spread the whipped cream onto the surface of the cake.
3. Carefully roll the cake with the cream tucked in lengthwise, removing the attached parchment (on the cake) and move it onto the new clean piece of parchment paper.
4. Wrap the cake up with the parchment paper and twist the ends to secure. Place onto a large rectangular plate and wrap with plastic wrap.
5. Set into the fridge to chill for at least 6 hours, or overnight.
6. Slice and serve chilled.