This homey dish from The Stray Dog in Minneapolis takes classic Minnesota hot dish to new levels. The tender brisket is braised in stout beer, while brown sugar helps caramelize the brussels sprouts. A creamy mushroom bechamel brings everything together, while the truffle-laced potato tots cap things off. You can braise the brisket, caramelize the brussels sprouts and cook the bechamel a day in advance if you like, then assemble the components, top them with potato tots and bake off the casserole when you are ready to eat this warming, hearty meal.
Preheat oven to 325°F. Sprinkle brisket all over with pepper and 1 tablespoon of the salt. Heat a large Dutch oven over high. Add brisket, fat cap down, and cook, undisturbed, until browned, about 3 minutes. Flip brisket, and cook, undisturbed, until browned on other side, about 3 minutes. Transfer brisket to a plate; set aside. Reduce heat under Dutch oven to medium-high. Add onion; cook, stirring occasionally, until softened, about 5 minutes. Add beer, and scrape up any browned bits from bottom of Dutch oven. Stir in broth, Worcestershire sauce, and remaining 1/2 teaspoon salt. Return brisket to Dutch oven. Bring mixture to a simmer over medium-high. Remove from heat. Cover and transfer to preheated oven. Braise in oven until meat is tender and easily pierced with a fork and a thermometer inserted into thickest portion of meat registers 190°F, 3 to 5 hours. Remove from oven; let cool in liquid, covered, for 1 hour. (Cooled, whole Braised Brisket can be stored in liquid in refrigerator up to 24 hours.)
Increase oven temperature to 425°F. Toss together Brussels sprouts, butter, brown sugar, salt, and pepper on a large rimmed baking sheet until evenly coated; spread mixture in an even layer. Roast at 425°F until Brussels sprouts are starting to brown and caramelize, about 10 minutes. Stir mixture, and continue to roast until Brussels sprouts are crispy on the outside and tender when pierced with a fork, about 5 minutes. Remove from oven. (Caramelized Brussels Sprouts may be stored in an airtight container in refrigerator up to 12 hours.)
Melt butter in a 13-inch oven-safe skillet over medium-high until sizzling. Add mushrooms; cook, undisturbed, until deeply browned on bottoms, about 4 minutes. Add onion, garlic, and 1 teaspoon of the salt; cook, stirring often, until mushrooms are deeply browned and tender, 6 to 8 minutes. Reduce heat to medium. Add flour; cook stirring constantly, until flour turns golden brown and smells nutty, 1 to 2 minutes. Slowly add milk, stirring constantly, until milk forms a thick paste with mushrooms and thickens into a gravy consistency, about 2 minutes. Remove from heat. Stir in pepper and remaining 1/2 teaspoon salt. (Use immediately, or store in an airtight container in refrigerator up to 12 hours.)
Reduce oven temperature to 375°F. Remove Braised Brisket from liquid, and cut into 1-inch chunks. Discard braising liquid. Add Caramelized Brussels Sprouts and 5 cups of the chopped Braised Brisket to Mushroom Béchamel in skillet; stir to combine. Reserve remaining Braised Brisket for another use. Toss together frozen potato tots, Parmesan, and truffle oil in a large bowl until combined. Arrange mixture in a circular pattern over casserole mixture in skillet to completely cover top. Bake at 375°F until tots are golden brown and crispy, about 30 minutes. Let cool slightly, about 10 minutes. Serve.