Need help recreating grandma's cornbread

My grandma passed away a few years ago and to my knowledge, her recipe book disappeared. She always made the best cornbread, which was much more dense than it typically comes out. The edges were crispy and chewy, and the middle was not fluffy or sweet in any way. I know it included the following:

• cast iron skillet

• jiffy mix

• crisco

I have tried using the box directions and using crisco, cast iron, etc., but I just can't seem to get it right. Do any of you make cornbread this way, and if so, what's your secret? Someone mentioned baking powder once, but I tried that before and it didn't make a difference.

Thanks in advance!