I can't say that my family has many heirloom recipes, and most are ones that appear at various Jewish holiday celebrations. Essentially, your standard Ashkenazi holiday foods, and occasionally foods of the type you'd expect to find in Romania, Hungary and Poland.
One recipe that has always been universally loved in my family (and by our friends) is my Mom's perhaps less traditional challah. It tends to be more honey forward and denser than your usual challah, and the dough is always too sticky to braid. But whenever my mom has served this challah, it's quickly gobbled up, and guests rave about it. Perhaps the fact that it's just a little different than your usual challah makes it so popular, but I love it anytime. And with the obvious honey flavor in the background, it's particularly suitable for Rosh Hashanah. And the sweet aromas of honey and bread that spread throughout the house as the challah is baking are intoxicating, in a very good way.
I've only recently begun making this challah myself, and I haven't quite nailed the texture - my mom's version is always denser. And maybe I don't need to get it quite right, but I preferred my mom's denser version. I suspect that a little less yeast, or perhaps a shorter rise, will accomplish the trick. Regardless, I'm very happy with the results.
The ingredients (for 2 loaves):
2 packages of yeast (I used instant, and might reduce quantity to 1 1/2 next time)
4 t kosher salt
1 3/4 C water
3/4 cup honey (make sure to use one you really like as the honey flavor/aroma really shines through in the finished bread)
7 C bread flour
3 eggs
1 1/4 C oil (my mom always used peanut, and so do I)
Mix, knead for 10 or so minutes (it will and should remain sticky), allow to rise according to yeast used in a greased bowl, and scrape into greased cake pans (or loaf pans, but you'll probably need 4). Use an egg wash -- one beaten egg mixed with a pinch or two of salt -- (I apply once, wait 10 minutes and apply again). Then bake at 350 degrees for about 50-60 minutes (I simply bake until interior of loaf registers about 190 degrees, which seems to take 50 minutes).
Here's what the loaves looked like pre-baking, post-egg wash (don't worry much about the shape, it will spread out perfectly on its own):

Here's a look at it fresh out of the oven, removed from the pan:

And finally, the interior:

As I noted above, the bread should be denser, not that I was disappointed with my results - I love the flavor. My mom may have overcome this issue by not letting the dough rise long enough, but I think I'll probably adjust the yeast downward my next try.