A pretty summer cake made with layers of white cake, alternating with layers of sweet and tangy rhubarb curd.
In a large mixing bowl, combine the cake mix, milk, melted butter, and egg whites. Using an electric beater, beat on medium high for two minutes.
Add 1/3 of the batter to a greased 8-inch springform pan. (If you have more than one pan, you can bake all three layers at once. Otherwise, bake one at a time, making three layers altogether. Bake at 350 degrees for 25 to 28 minutes, or until light golden brown on top. A cake tester should come out clean. Set the cake layers aside to cool on a cooling rack.
Combine the chopped rhubarb, raspberries, water, sugar, and lemon juice in a medium saucepan. Heat over medium-high heat until boiling, reduce to a simmer and simmer gently for 10 to 15 minutes, or until rhubarb is soft.
Remove rhubarb mixture from heat and blend in a blender or food processor. Return the mixture to the saucepan, reserving about 1/3 to 1/2 cup of the mixture to set aside.
Combine the reserved mixture with the egg yolks and the corn starch; whisk together thoroughly.
Begin heating the mixture in the saucepan until it again comes to a boil. Reduce heat to a simmer. Slowly add the rhubarb/egg yolk mixture in with the rhubarb in the saucepan, whisking constantly for 2-3 minutes so that no lumps form. Continue simmering for about 10 minutes, stirring frequently, until the mixture is reduced and thick. Remove from heat and set aside to cool. Chill for several hours before using on the cake.
In a medium mixing bowl, mix together the cream cheese, butter, powdered sugar, and vanilla until smooth and creamy. Set aside.
Have the (cooled) cake layers, the (chilled) rhubarb curd, and the cream cheese frosting all ready and at hand. Trim two of the three cake layers, if necessary, so that they are completely flat on top.
Place the first cake layer on desired cake plate. Spread a 1/2 inch thick layer of rhubarb curd on top. Place the second cake layer on top, and repeat, spreading with another layer of rhubarb curd. Place the final layer on top, and spread with cream cheese frosting. Decorate with raspberries, mint leaves, and edible flowers. Serve immediately, if possible, or else chill until ready to serve. Serves 10.