Boston Market Cornbread: 1 box Jiffy Mix Cornbread Mix & 1 box Jiffy Mix Yellow Cake Mix - OR - 2 boxes Jiffy Mix Cornbread Mix, 1 box regular yellow cake mix. Mix both boxes according to directions. If you have only boxes of Jiffy Mix, use a brownie sized baking pan, 8x8", if you are using a box of regular cake mix, use a 9x13" pan. Spray pan, bake @ 350, approx. 30 mins.