Just for Cecily: Grandma's (Lunch Lady) Peanut Butter Squares Recipe

I'm not sure if this is the recipe I tried a million years ago, but the one I made turned out really good and this looks very similar. The only thing I am confused on is the 16 ounces of confectioner's sugar for the frosting--in fl oz that would be two cups. Is this what the recipe means??



Ingredients :

Squares:
1/2 cup solid vegetable shortening
1/2 cup margarine
2 cups all-purpose flour
1 cup firmly packed brown sugar
1 cup uncooked quick oats
1/2 teaspoon baking soda
1/2 teaspoon salt
1 heaping tablespoon chunky peanut butter
2 heaping tablespoons creamy peanut butter


Frosting:
6 tablespoons butter, softened
1 1/2 teaspoons vanilla extract
1/4 cup cocoa powder
1/2 teaspoon salt
16 ounces confectioners’ sugar
1/4 cup milk


Instructions :
Preheat the oven to 350 degrees. Lightly grease a 13 x 9-inch baking dish. In a large bowl, mix the shortening, margarine, flour, brown sugar, oats, baking soda, salt, and peanut butters until well blended and crumbly. Press into the prepared baking dish. Bake for 20 minutes. Turn off the heat, and leave the pan in the oven for 5 minutes longer. To prepare the frosting, combine the butter, vanilla, cocoa, and salt in a medium-size bowl. When smooth, alternately add the sugar and milk. If the frosting is too thin, add a bit more sugar. For thinner frosting, add more milk (just 1 tablespoon at a time). Stir until creamy. Frost the peanut butter squares while warm.