Spiced Pumpkin Bars with Cream Cheese Frosting

Name: Spiced Pumpkin Bars with Cream Cheese Frosting
Ingredients: 3/4 cup butter, melted; 1/2 cup white sugar; 1/2 cup dark brown sugar, packed; 2 cup pumpkin puree; 3 large eggs; 1.25 cup all purpose flour; 3/4 cup whole wheat pastry flour; 2 teaspoon baking soda; 1 teaspoon cinnamon; 1/2 teaspoon salt; 1/2 teaspoon ground ginger; 1/2 teaspoon ground cloves; 1/2 teaspoon allspice; 1/4 teaspoon nutmeg; 1 teaspoon pure vanilla extract; 1 8-ounce block of cream cheese, at room temperature; 1 stick of unsalted butter, at room temperature; 3.5-4 cup powdered sugar (sift sugar if lumpy); 2 teaspoon pure vanilla extract; 1-2 tablespoon milk (optional)