I've done freezer cooking. Still do, when it suits. Done OAMC. Still do, when it works out. This is one variation of pre-cooking that we use.
My daughter made up these brownie mixes that are just as good (or better) than the store-bought cookie/brownie mixes. She used the recipes found here and combined dry ingredients in glass jars. The pint jar contains ingredients and instructions for the small batch (9X9 or so) and the quart jar is a double batch.
Instructions on the lids are just on little Post-it type sticky notes, with amounts of wet ingredients, temperature and time. We all know how to mix it up, right??!
SO easy to just dump in a bowl, add eggs/oil and stick in the oven for afternoon snack or even a quick dessert, since I usually forget to consider that. ;)
