Heat oven to 350 deg. Lightly spray 2 13x9 inch pans. Line with wax paper;spray paper. In a large bowl,combine white cake ingredients;beat at low speed until moistened. Beat 2 minutes at high speed. Pour half of the batter into each waxed paper-lined pan.
In same bowl,combine lemon cake ingredients;beat at low speed until moistened. Beat 2 minutes at high speed. Spoon half of the lemon batter into each pan over the white cake batter. Using a knife,swirl lemon batter through white.
Bake 30 to 40 minutes or until tests done. Cool in pans on rack 10 minutes;remove from pans. Peel off wax paper;cool completely.
To assemble cake,place one cake,top side down on serving plate;top with lemon curd. Place 2nd cake top side up,on filling. Cover;chill at least 1 hour before frosting.
Combine frosting ingredients. Beat until stiff peaks form. Frost sides and top of cake. Garnish with lemon slices.