Make the cake: Preheat the oven to 350 degrees F. Coat a 13-by-18-inch rimmed baking sheet with cooking spray; line with parchment, then spray the parchment. In a medium bowl, whisk the flour with the cocoa powder and baking powder. Set aside.
Beat the egg whites with a mixer on high speed until foamy. Beat in the cream of tartar and salt, then slowly beat in 1/2 cup granulated sugar. Increase the speed to high; beat until stiff shiny peaks form, 2 to 3 minutes. Transfer the meringue to a separate bowl.
In the same mixer bowl (leave it dirty!), combine the egg yolks, vanilla and the remaining 1/2 cup granulated sugar. Beat on high speed until light and doubled in volume, about 2 minutes. Beat in the water and canola oil.
Sift the flour mixture into the egg yolk mixture, then stir with a rubber spatula until just combined.
Add the food coloring to the batter and beat on high speed until smooth and bright red, about 1 minute.
Stir a dollop of the meringue into the batter using a rubber spatula. Add the remaining meringue and gently fold into the batter until no white streaks remain.
Transfer the batter to the prepared baking sheet; spread evenly with an offset spatula. Tap the bottom of the pan firmly against the counter to remove any air bubbles.
Bake until a toothpick inserted into the center of the cake comes out clean, 15 to 20 minutes. Immediately loosen the edges with a paring knife.
Dust the cake with confectioners' sugar, working quickly while the cake is still warm.
Lay a clean kitchen towel (not terry cloth) over the cake. Place another baking sheet on top of the towel.
Invert the cake onto the towel. Remove the pan and peel off the parchment.
Starting at a short end, roll up the cake and towel together into a log. Keep the cake rolled up until it has cooled completely.
Unroll the cake (it's OK if the end is still curled up). Cut the cake into 3 long strips, each about 4 inches wide. Use a ruler to make sure they're even.
Spread an even layer of frosting on each strip of cake (use a little less than one-third of the frosting). Make sure to get frosting under the curled end.
Make the frosting: In a clean mixer bowl, beat the cream cheese and confectioners' sugar on medium-high speed until smooth, about 2 minutes. With the mixer on low speed, add the vanilla and heavy cream. Slowly increase the speed to high and beat until smooth.
Roll up one of the strips into a tight spiral.
Move the spiral over to the next strip so that the ends meet and roll up into a fatter spiral. Continue with the third strip to make a large spiral.
Turn the cake flat-side down and place on a cardboard round or platter. Gently squeeze the spiral together to make sure it's compact.
Cover the cake completely with a thin layer of frosting, using the frosting to cover the seam of the spiral. Refrigerate 30 minutes.
Return the cake (without the cardboard round) to your workspace and cover completely with the remaining frosting using an offset spatula.
Place a star-shaped cookie cutter on top of the cake. Sprinkle some blue sanding sugar inside the cutter (use a small brush to help distribute the sugar), then carefully lift the cutter. Repeat to make more stars in different sizes. Refrigerate until ready to serve.
When you slice into the spiral, you see vertical stripes!