Stir together first 3 ingredients and 1 cup sugar in a large bowl. Make a well in center of mixture; add oil, next 2 ingredients, and 1/4 cup water. Beat at medium-high speed with an electric mixer 3 to 4 minutes or until smooth.
Beat egg whites and cream of tartar at medium-high speed until soft peaks form. Gradually add remaining 1/4 cup sugar, 1 Tbsp. at a time, beating until stiff peaks form. Gently stir one-fourth of egg white mixture into flour mixture; gently fold in remaining egg white mixture. Spoon batter into 6 greased and floured 8-inch round cake pans.
Bake at 350 for 12 to 15 minutes or until a wooden pick inserted in center comes out clean. Cool in pans on wire racks 10 minutes; remove from pans to wire racks, and cool completely (about 1 hour).
Spread filling between cake layers, leaving a 1/4-inch border around edges (about 2/3 cup between each layer). Cover cake with plastic wrap, and chill 8 to 24 hours.
Spread Strawberry Frosting on top and sides of cake. Chill 2 hours before serving.
