Cover a baking sheet with parchment paper; secure with masking tape, and set aside.
Beat egg whites (at room temperature) and salt in a bowl at high speed of a mixer until foamy. Gradually add 1/2 cup sugar, 1 tablespoon at a time, beating until stiff peaks form (do not underbeat). Add vanilla, and beat until blended. Spoon meringue into a pastry bag fitted with a large star tip. Pipe into 60 portions onto prepared baking sheet, forming pointed mounds 1 inch wide and 1 inch high.
Bake at 200° for 1 hour or until dry. Turn oven off, and let meringues cool in closed oven at least 12 hours. Carefully remove meringues from paper.
Combine 2/3 cup sugar, cornstarch, and lemon rind in a saucepan; stir well. Gradually add water and lemon juice; stir with a wire whisk until blended. Bring to a boil over medium heat; cook 1 minute, stirring constantly. Gradually stir one-fourth of hot lemon mixture into egg yolk; add to remaining lemon mixture, stirring constantly. Cook over medium heat 1 minute or until thickened, stirring constantly. Pour lemon custard into a bowl; place plastic wrap on surface, and chill.
Spoon 2 tablespoons lemon custard onto each of 10 dessert plates, and top each with 6 meringues. Arrange 2 tablespoons raspberries and 2 tablespoons blueberries on each plate. Garnish with currants and edible flowers, if desired.
Note: You can store baked meringues in an airtight container for up to 2 days.