Carrot Sheet Cake with Cream Cheese Frosting

Cooking spray

9 tablespoons butter , softened

cup packed brown sugar

1/2 cup granulated sugar

2 large egg s

2 large egg whites

2 cups all-purpose flour

2 teaspoons baking soda

1 teaspoon ground cinnamon

1/4 teaspoon salt

3/4 cup low-fat buttermilk

2 cups finely shredded carrot Frosting:

1/2 cup (4 ounces) block-style fat-free cream cheese

1/4 cup butter , softened

2 teaspoons vanilla extract

teaspoon salt

2 3/4 cups powdered sugar , divided

1 tablespoon orange sugar sprinkles