Beat the butter with the powdered sugar until creamy. Rinse the rose petals, pat dry, and finely chop. Mix the rose water into the butter, then gently stir in the petals. Form the butter into a roll, then wrap in aluminum foil. Chill in the refrigerator for at least 1 hour. Remove the butter from the refrigerator, unwrap, and roll in the cane sugar.
For garnish, brush some rose petals with egg whites and sprinkle with sugar. Set aside and let dry.