To your 4 cups of riced potatoes, add 1/4 cup butter in pats so it melts in evenly. Stir a few times to get the butter mixed in well. Cover and refrigerate overnight. If you would like to cook the same day you can cover the potatoes with a towel and set aside on your countertop until they are completely cooled. Or to cool faster, place uncovered in refrigerator for 30 minutes, pull out and stir, refrigerate 30 minutes longer, stir. Keep repeating until cooled. Even faster? Use the freezer. Same process: freezer, stir, freezer, stir until cool.
Note: If you can, let the potatoes cool off a bit at room temp before covering. If they are still steaming hot, all that steam will condense on the lid and give you extra water.