Good afternoon. Kristen if you are referring to Miss Rose’s fruit cake recipe on page 65/66 in the TCB edition…that cake weighs just short of 24, oz. A 9 inch X 5 inch X 3 inch loaf pan can fit exactly 2X that amount.
I will go thru the Math with you.
9x5=45 X 3 inch deep=135 Divide by 2=67.5 X by .75 = 50.625 oz. of batter. will fit allowing for75% filled for the chemical leaveners doing their thing.
Kristen if you wish to do a one recipe you will have to find a smaller pan or make muffins .
I hope this info helps you make the right decision for yourself.
Good luck & enjoy the rest of the day young lady.