Crust: Mix 1 cup sugar, butter, egg yolks, flour and baking powder. Pat into tin and bake 10 minutes or until browned in a moderate (350 degree) oven.
Filling: Mix together 1 cup sugar and cornstarch. Add blueberries, lemon juice and water in a double boiler. Stir in sugar/cornstarch mixture and cook until mixture thickens. Cool and spread on crust.
Meringue: Beat egg whites, 1/2 cup sugar, vanilla and salt until stiff peaks form. Spread on cooled filling and cover with walnuts. Brown in 400 degree oven.