Hi Pat,
Just use one 6 to 8 oz cornbread mix for the recipe. The Jiffy mix will do just fine, I use that most of the time! I do believe that I use the Jiffy "Corn Muffin" mix which is 8 1/2 oz size. It really doesn't matter much, the batter bakes up a lot like spoon bread. You just go on and fix this up. It's not one of those "particular" type recipes where everything has to be "juz' perfect", as are a lot of southern recipes. LOL....Enjoy, and dont forget the fresh butter and home grown tomatoes with this, it really is a wonderful summer type dish.

Peace To You, Pat.
And, Peace To All On TKL,
David In Virginia