Beat egg whites until frothy; add cream of tartar and beat at high speed until soft peaks form. Gradually add 3/4 cup sugar; continue beating until stiff but not dry. Set aside.
Beat yolks about 3 minutes or until very thick and light in color. Add remaining sugar 1 tablespoon at a time; beat until thick. Add orange juice and peel; blend until smooth.
Thoroughly combine flour, finely chopped pistachios and salt; gently fold into egg yolk mixture until well-blended.
Fold yolk mixture into beaten whites.
Pour into 6 (5 3/4 x 3 1/4 x 2 1/4 inch) ungreased pans; cut through batter with spatula to remove air bubbles. Bake at 325 degrees F. 25 to 35 minutes or until cakes spring back when lightly touched.
Immediately invert pans on wire racks; cool completely. To remove cakes, loosen around edges of pans with knife. P.
our Orange Syrup over cakes; allow to sit until syrup is absorbed. Or, optionally frost with a Fluffy White Buttercream Icing. Garnish tops of cakes with chopped pistachios.
Combine 3/4 cup each sugar and water and 1 teaspoon orange peel; bring to boil. Simmer, uncovered, 2 minutes; cool 10 minutes. Makes 1 cup.
Orange Buttercream Icing can be substituted for Orange Syrup. Combine 3 cups powdered sugar, 6 tablespoons softened butter, 5 tablespoons half-and-half or milk and 1 teaspoon grated orange peel. Spread about 1/4 cup over top and sides of each cake. Garnish with chopped natural California pistachios. Makes 1 3/4 cups.