Nonstick cooking spray, for the pan
One 15.25-ounce box white cake mix
1 1/2 teaspoons vanilla extract
3 large egg whites
1 stick (8 tablespoons) unsalted butter, melted and cooled
One 8-ounce package cream cheese, at room temperature
1 1/2 teaspoons vanilla extract
3 large egg whites
4 tablespoons unsalted butter, melted and cooled
3 cups confectioners' sugar, plus more for dusting
1/2 cup multicolored sprinkles, plus more for garnish
Vanilla ice cream, for serving