Heat oven to 325. Generously spray bottom of 10-12 inch springform pan with baking spray (with flour).
In a large bowl, beat cake ingredients on low speed 30 seconds; increase speed to medium and beat 2 minutes. Pour batter into prepared pan. Bake a 10 inch pan 45-50 minutes, a 12 inch pan 35-40 minutes. Top of cake may appear very dark brown and rippled with a crack in center of cake. Cool completely, 1 hour.
Carefully run knife around side of pan to loosen, remove side of pan. Transfer cake to serving plate. In medium bowl, combine frosting ingredients; frost cake. Garnish with orange peel. Store loosely covered in refrigerator.