To make the raspberry mousse filling, in a small bowl mix gelatin with 1 tablespoon of water. Let sit for 5 minutes.
Microwave ¼ cup of heavy whipping cream until hot, about 30 seconds.
Add bloomed gelatin into the hot cream and stir until dissolved.
Place the chopped chocolate in a small bowl and pour hot cream with gelatin over it. Let it stand for a minute and stir until chocolate is fully melted. If needed, microwave for 30 seconds. Cool completely. (You can put it in the fridge for a few minutes while working on the next step.)
In a mixing bowl with whisk attachment, beat the remaining heavy whipping cream until hard peaks form.
Add cooled white chocolate mixture and raspberry jelly into the whipped cream and carefully fold until well combined. Refrigerate while making the cake.
To make the cake, preheat the oven to 350°F (177°C). Line a 9×13-inch baking sheet with parchment paper. Spray with cooking spray.
Separate the eggs.
In a mixing bowl with whisk attachment, combine egg whites and ¼ cup of sugar. Beat until hard peaks form.
In another mixing bowl with whisk attachment, combine egg yolks and the remaining ¼ cup of sugar. Beat the mixture until thick and pale yellow.
Add milk and mayo and give it a good mix until smooth.
Add flour and cocoa and mix for another 30 second or so, until the mixture is smooth.
Add half of the beaten egg whites and gently fold until mostly smooth. And then fold in the remaining egg whites and fold until the batter is nice and smooth.
Pour the batter into the prepared baking sheet and spread evenly.
Pour 1 cup of hot water into an empty pan and place on the lower rack.
Place the cake on the middle rack and bake for about 13 minutes, or until the toothpick comes out clean.
Cool the cake in the pan on wire rack. It takes 15-20 minutes. (If you can’t get to it within 30 minutes to move forward with following steps, make sure to cover it with a towel to prevent drying the cake.)
Dust powdered sugar on a clean kitchen towel on the counter.
Once the cake is completely cooled, very carefully invert the cake onto the prepared kitchen towel. Peel off the parchment paper, and cut the edges off.
Spread raspberry jelly all over the cake.
And then spread raspberry mousse, reserving about ½ cup of filling for decorating. Spread thinner layer of filling on outer end of the cake.
Then carefully roll the cake into a log from long end, lifting the kitchen towel to gently push the cake up and over, so that the ends meet at the base.
Gently pup the roll on a wire rack placed on a baking sheet.
To make the ganache, in a small saucepan, bring heavy cream to a simmer. Do not boil. Pour hot cream over chocolate chips, and let it sit for good 2 minutes. Then mix well until smooth for couple minutes.
Immediately pour the ganache over the cake, letting it drip onto the baking sheet. Place the cake in the fridge for at least 2 hours.
To decorate the cake, place the reserved mousse filling into a piping bag with decorative tip. (I used Wilton 1M.) Pipe rosettes on top and top with fresh raspberries.