Let me be honest. I dreaded having to make this meal. I put it off for as long as I could, and then I couldn't really justify it anymore. And then I dreaded making it while I made it. Ok, so maybe not that badly. There really is something cathartic about chopping veggies. It's just...there's SO much to juggle with this recipe. I'm not even going to post it all out here. You can find it here, courtesy of Bon Appetit via Epicurious. Even the recipe recommends making it over the course of several days (it takes 2 hours, give or take). I recommend a willing helper.
I will point out that taking heed of the comments and reviews is useful. I halved the recipe based on the recommendations in the reviews, and the dish still overflowed. The veggies I used were baby turnips, parsnip, carrots, Cremini and button mushrooms, and butternut squash (Get pre-cubed. Thank me later.), in addition to the potato topping and the (fresh) pearl onions in the veggie mix, plus the onion in the sauce. Do not neglect the white wine, rosemary, tomato paste, or the miso/tamari soy sauce. This really made the flavor.
Even my husband, who is an avowed meat-lover, said that it was more flavorful than most shepherd's pies he's had before. And although shepherd's pie is, I believe, a traditionally English dish, I kept thinking of France as I enjoyed the blend of flavors. Either way, it's really good. It's just up to you to decide if it's worth the labor.