Bison Shepherd's Pie with Potato Crust

Method

1. Put the potatoes in a large pot, cover with the water, stir in the 1 tbsp salt for the potato water and bring to a boil. Cook until a knife slips in easily, 15 to 18 minutes, then drain and let them steam dry in the pot for 2 minutes. Mash with the butter, warm milk, 1½ tsp of the divided salt and half the pepper.
2. Heat the oven to 400°F. Heat the oil in a 12-inch skillet over medium-high and brown the bison in two batches, about 5 minutes each, breaking it up, until deeply browned. Set it aside.
3. In the same skillet over medium heat, cook the onion, carrot, celery and mushrooms for 8 minutes. Stir in the garlic and tomato paste for 2 minutes, then the flour for 1 minute.
4. Pour in the broth and Worcestershire and simmer 5 minutes, until thick. Return the bison with the thyme, the remaining 1½ tsp salt and the remaining pepper. Taste, adjust the salt, then spoon the filling into a 9x13-inch baking dish.
5. Spread the potatoes over the top to the edges and rake a fork across the surface. Sprinkle with the cheddar and bake 25 minutes, until the filling bubbles at the edges and reads 160°F in the center.
6. Broil 2 to 3 minutes until golden, then rest 10 minutes before serving.