1/3 cup all purpose flour
1 tablespoon Hungarian sweet paprika
1 1/2 teaspoons coarse kosher salt
1 teaspoon freshly ground black pepper
1 1/2 lbs pounds ground bison
1/3 lb rindless slab bacon, cut crosswise into 1/2-inch-thick slices
2 tablespoons (or more) olive oil (we omit this and just cook the bison in the bacon grease)
1 cup chopped onion
1/2 cup peeled chopped carrot
1/2 cup chopped celery
1/2 cup peas
1/2 cup corn
3 garlic cloves, chopped
2 cups dry red wine (such as Syrah)
1 cup low-salt chicken broth
1 cup canned crushed tomatoes
2 bay leaves
1 teaspoon chopped fresh thyme
1 teaspoon chopped fresh sage
5 lbs russet potatoes, peeled, quartered
3/4 cup whole milk
1/2 cup (1 stick) unsalted butter
1 teaspoon coarse kosher salt
1/2 teaspoon freshly ground black pepper
1 large egg, beaten to blend
1 large egg
1 tablespoon water
1 cup finely grated Parmesan cheese (we've also used sharp cheddar and English cheddar with caramelized onions)
Whisk first 4 ingredients in large bowl. Add bison; toss. Heat large pot over medium heat. Add bacon; cook until crisp. Transfer to paper towels. Add 2 tablespoons oil to (or simply use bacon drippings already in) pot; increase heat to medium-high. Working in batches, cook bison until browned. Return to same bowl. Add chopped onion, carrot, celery, and garlic to pot; cover and cook until vegetables soften, stirring occasionally, about 5 minutes. Add wine; bring to boil, scraping up any browned bits. Add broth, tomatoes, bay leaves, thyme, sage, reserved bacon, and bison. Reduce heat to low. Cover; simmer until bison is tender, stirring occasionally, about 15 minutes. Add peas and corn, remove from heat. Season with salt and pepper, if needed.
For mashed-potato crust:
Cook potatoes in large pot of boiling lightly salted water until tender, 18 to 20 minutes. Drain. Return potatoes to pot; add milk and butter, 1 teaspoon coarse salt, and 1/2 teaspoon pepper and mash until smooth and slightly cooled, about 2 minutes. Whisk in egg.
Preheat oven to 400°F. Spoon bison filling into two 3-quart (13x9x2-inch) baking dishes. Spoon mashed potatoes over; smooth top to cover completely.
Beat egg and 1 tablespoon water to blend. Brush over potatoes, then sprinkle cheese all over.
Bake pie until top is browned and filling is heated through, 30 to 40 minutes (50 to 60 minutes if chilled). Let rest 10 minutes.
DO AHEAD: Can be made 1 day ahead. Cover and chill. Alternatively, make the filling ahead of time and freeze it. Then make the potatoes the day of, assemble, and bake.
Adapted from Bison and Red Wine Shepherd's Pie by Bruce Aidells, Bon Appétit February 2010