A friend gave me a recipe for honey bun cake, and also a finished cake.   Hers was so moist it seemed almost wet, but when I made one it was like a typical packaged cake, rather dry.   Also, hers seemed bumpy on top, whereas mine was smooth.     My question is - would baking it for a shorter time help?  Or maybe a lower temperature?   Or does overmixing affect the moistness?   I couldn't believe that with 1 cup of sour cream and 1/3 cup of honey added to a packaged mix, it could be so dry!

--Paul

The first question I would have is how old was the finished cake that she gave you.  Honey is hygroscopic, meaning it is able to pull moisture out of the atmosphere.  A cake made with honey may seem dry immediately upon leaving the oven, but over time will absorb moisture from the air.

Some of the variation in quality may be explained, as you suggest, by over-mixing although it sounds like you were altering a standard cake mix.  Makers of cake mixes choose the flour they use and other ingredients to minimize the effects of mixing the batter more than necessary.

In scratch baking, if you use an all-purpose flour and mix it too much, you encourage the formation of glutens which will change the texture and rise of the cake.  It is always preferable to use cake or low protein flour, if possible, and always mix just the minimum time needed to thorougly blend the ingredients.  That is why many cake recipes call for mixing the wet ingredients in one bowl and the dry in another, and then folding the dry into the wet, a third at a time.  This method makes it more difficult to over-mix.

It is hard to say whether cooking the cake for a shorter time would help.  The best way to know if a cake is done is to test for doneness by inserting a toothpick into the center and pulling it back out.  If it is wet, the cake is likely not done (with the exception of lava cakes which are intentionally undercooked in the middle).  With the altered ingredients, the toothpick might still appear to be a bit wet, but if there are cake crumbs adhered to it, as well, it is probably done, or near to done.

As for oven temperature, the rough appearance of your friend's cake suggests that it may have been cooked at a higher then usual temperature, either because the recipe says to do so, or because her oven runs a bit hot.  Too hot an oven will cause the outside of the cake to set well before the inside has finished expanding.  The result is a cake that is uneven, that swells in the middle or that cracks.  It may also be that your oven runs a bit colder than the set temperature.

Actually, my guess (without having seen or tried the actual recipe) is that your cake may have been a bit over-cooked, but is likely closer to the correct result.