Shepherd's Pie is definitely comfort food. We in the West aren't really in comfort food "season" yet, but to be honest, this is one of those dishes that my family eats year-round, because it's just tasty and never fails to hit the spot.
I think every family has their own spin on what should go into this dish (my mom, for example, only ever had meat, the mash topping, and usually some cheese), but some Shepherd's Pie staples are ground meat of some kind, carrot, peas, and maybe potatoes. I've seen a lot of recipes that call for gravy mixtures, and others that contain Worcestershire. Some folks, like mama, add cheese to the top, others don't. All-in-all, I think this dish is so basic that it can honestly contain whatever you want.
My goal in this version was to create something that hit most of the "standard" notes. Ground meat, a savory sauce (with some complimentary herbs, and liquid smoke to provide something akin to umami), a few compliant, chunky veggies mixed in to provide some texture, and a creamy mashed topping.
All those essential boxes are checked!
Notes: If you wanted to play with different ground meats, like ground lamb for instance, feel free. You could change up some of the veg, too, by adding some diced daikon radish or turnip, but keep in mind that changes the carb count. If you have an herb blend you really like, feel free to use it. My only seasoning recommendation is to be sure to keep the liquid smoke and the black pepper. The flavor simply isn't quite right without them.