Preparation

• Preheat the oven to 325°F. Sift half of the sugar with the flour and the salt. Set the remaining sugar aside. In a large bowl, whip the egg whites with a mixer to thoroughly combine them. Add the vanilla extract and the cream of tartar. Slowly add the reserved sugar into the mixture, beating continuously at medium speed. When soft peaks begin to form, sift half of the flour mixture in so that it dusts the top. Fold the remaining flour in very gently. Continue until all of the flour mixture is incorporated.
• Carefully spoon the batter into a tall ungreased tube pan. Bake for 35 minutes. Check for doneness with a wooden skewer. It should come out dry. Cool upside down on a cooling rack for 1 hour before removing the cake from the pan.
• Whip the cream with a mixer until stiff. Divide into three parts. Add the blueberry purée to one part, raspberry purée to the next, and leave one as is. Cut the cake into three horizontal parts with a long serrated knife. Place the red cream on the bottom layer and top with the next cake layer. Place white cream on top of the second layer and then top with another cake layer. Finish with the blue cream.