With an electric mixer on high speed, beat the egg whites, cream of tartar and salt until soft peaks form when the mixer is removed from the batter.
Add half of the remaining sugar and beat for 1 minute. Add the remaining sugar, 2 tablespoons at a time, beating after each addition.
Stir in the vanilla.
Fold the flour and sugar mixture into the egg whites, 1/4 cup at a time, just until incorporated.
Put the batter in an ungreased 10" tube pan and bake until the cake is light golden brown and springy to the touch, about 1 hour. Invert the pan and let the cake cool completely before removing from the pan.
For the Summer Fruit Salad:
Mix fruit in a bowl.
Sprinkle with the orange juice.
For the Finest Raspberry Dessert Sauce:
Puree the berries in a blender with the lemon juice. Blend in the sugar by the tablespoonful, tasting after each addition, until the desired degree of sweetness is reached.
Strain through a fine strainer, pressing with a rubber spatula to release the juices.
Put it all together:
Place a slice of angel cake on each plate. (Store the leftover cake in an airtight container or freeze for longer storage.)
With a slotted spoon, place a portion of the Summer Fruit Salad on a corner of the cake slice and let it spill over the side.
Drizzle the raspberry sauce around the fruit salad.