Slow-braised top sirloin roast in a rich Diet Pepsi and beef broth sauce, shredded and tossed with pappardelle, mushrooms, tomatoes, cream, and spinach.
Salt the roast generously on all sides and refrigerate uncovered for 4 hours to dry brine. Remove from the fridge and bring to room temperature before cooking.
Heat olive oil in a Dutch oven over high heat. Sear the roast on all sides until deeply browned. Remove and set aside.
Reduce heat to medium. Add butter, chopped shallots, and minced garlic to the same pot. Sauté until fragrant.
Add the Diet Pepsi, Worcestershire sauce, soy sauce, Dijon mustard, honey, tomato paste, beef broth, concentrated chicken broth, onion powder, garlic powder, paprika, salt, and pepper. Stir to combine.
Return the seared roast to the pot. Add bay leaves and fresh thyme sprigs.
Cover with a lid and bake at 325°F (165°C) for 4 hours, until the beef is fork-tender.
While the roast braises, sauté the sliced mushrooms in butter in a separate skillet until golden. Set aside.
Remove the roast from the pot and shred with two forks. Ladle some braising broth over the shredded beef to keep it moist.
Strain the remaining braising broth into a large deep pan or pot and bring to a simmer.
Add the pappardelle and chopped baby tomatoes to the simmering broth. Cook for about 7 minutes until the pasta is al dente.
Stir in the heavy cream, spinach, parsley, and sautéed mushrooms. Cook until the spinach is just wilted.
Add the shredded beef (half the roast works well, save the rest for another use) and toss to combine.
Finish with grated Parmesan and a squeeze of lemon. Serve immediately.