Roasted root vegetable and mushroom shepherdess pie, version 3

We loosely followed this recipe: https://www.seriouseats.com/recipes/2012/11/mushroom-and-root-vegetable-shepherds-pie-recipe.html Based on our pantry during the pandemic, we tried this with 16 oz cremini mushrooms, 2 carrots, 2 medium Korean sweet potatoes, 2 purple-topped turnips, and 2 large shallots which we tossed with corn oil, salt, black pepper, and a dash of marash pepper, then oven-roasted for 30 mins (mushrooms on one baking sheet) and 40 mins (root vegetables spread in a single layer on two baking sheets). To substitute for roasted jicama, we added 8 oz sliced water chestnuts (rinsed, drained, towel-dried, and cut into half-moons) to the roasted mushroom-vegetable mixture. For the sauce, we used 2 leeks (cut into half-moon slices) and 4 stalks diced celery along with 1 small rosemary sprig (about 2 inches, leaves minced) and 2 large sage leaves (julienned). Instead of the vegetable broth, we used 3 cups beef broth (so our version was not vegetarian). At the end of simmering the sauce, we seasoned to taste with 1 Tbsp Worchester sauce, 1 Tbsp aged red wine vinegar, 1 ½ tsp soy sauce, 2 tsp sugar, and a dash each salt and black pepper. We then slowly folded the sauce into the roasted vegetable, mushroom, and water chestnut mixture in a large mixing bowl. We used all of the sauce for the amount of roasted vegetables we had (see Note below). For the mashed potato topping, we used 6 medium and 3 small Yukon potatoes, which we boiled until fork-tender and then mashed with about 6 Tbsp butter and 1/3 cup hot milk. We sprayed a 9×12″ baking dish, placed the filling (roasted mushroom vegetable mixture with sauce), then topped with the mashed potatoes. We baked at 375 for 35 mins. (Aug. 2020)Note: We used about 7/8 of the roasted vegetable, mushroom, and water chestnut filling combined with the leek/celery sauce. We saved the remainder in two one-cup containers to freeze; we will try them as filling for handheld puffed pastry at a later time.