To make the cake, preheat the oven to 350°F (177°C). Line bottom of 1 9-inch springform pan (at least 3 inches tall) with parchment paper. No need to grease the pan.
Separate egg whites and yolks, making sure not even a little bit of egg yolk gets into the whites. (Tip: It’s easier to separate the egg when they’re cold right out of the fridge.)
In a mixing bowl with whisk attachment, whisk together egg yolks and ½ cup of sugar until pale and tripled in volume, about 5 minutes.
Meanwhile, sift flour and salt.
In another mixing bowl with whisk attachment, beat egg whites at medium low speed until foamy.
Stir in cream of tartar, if using.
Add remaining ½ cup of sugar 1 tablespoon at a time and continue to whisk until stiff peaks, gradually increasing the speed to medium high, 7-10 minutes.
Using a spatula, add 1/3 of the whipped egg whites into the egg yolk mixture and gently fold until mostly smooth. Add the remaining egg whites and gently fold until smooth.
Add sifted flour into the batter in 3 stages, whisking the batter well after each addition.
Pour the batter into prepared pan and smooth the top.
Bake the cake until inserted toothpick comes out clean, about 40 minutes. Don’t open the oven for at least the first 30 minutes!
Let the cake cool for 5 minutes in the pan. Then run a knife around the edges and invert onto a cooling rack. Cool completely. Once cooled, wrap with plastic wrap and refrigerate, preferably overnight. It’ll be easier to slice it when the cake is thoroughly chilled.
To make raspberry jello layer, spray two 7-inch round cake pans with a cooking spray.
In a small bowl mix together gelatin powder and water. Let it sit for 5 minutes.
In a small saucepan, combine raspberries and sugar. Cook it over medium high heat, until sugar is melted, stirring frequently and mashing the berries.
Stir in gelatin and cook over medium low heat until the gelatin is fully melted.
Run the mixture through a sieve to remove seeds. Divide the mixture into the prepared pans. Refrigerate for 2-3 hours, or overnight to set.
To make the simple syrup, in a small saucepan, combine 1 cup water and sugar. Bring it to a boil and simmer until sugar is fully dissolved. Remove from heat and cool completely.
To make the cream cheese frosting, beat cream cheese and butter on medium high speed until fluffy, about 1 minute.
Add powdered sugar and vanilla extract. Beat on low speed for a minute. Then increase the speed to medium high and continue to beat until smooth and fluffy, about 3 minutes.
Transfer the frosting into a large frosting bag. You can use a round piping tip, if you have it, but it’s not necessary.
To assemble the cake
, slice the cake into 3 even layers. (I use this cake slicing kit
, but this’s a cheaper version
Place the bottom cake layer on a serving platter. (TIP: Place 3 strips of parchment or wax paper on the bottom to keep the serving platter clean.) Brush on 1/3 of chilled simple syrup evenly on the cake. Pipe the cream cheese frosting all over and smooth it with an offset spatula. Place the raspberry jello in the middle. Pipe frosting around the jello, creating a border. Pipe more cream cheese frosting over the jello and spread evenly with an offset spatula. Place the next cake layer and repeat.
Place the top cake layer upside down so that the top of the cake is nice and flat. Coat the entire cake with frosting and smooth it with an offset spatula.
Mix the remaining cream cheese frosting with freeze-dried raspberry powder and decorate the cake as desired. I used Wilton M1 piping tip
to pipe the decoration on top.