Sprinkle both sides of meat with kosher salt. Place a wire rack in a rimmed baking sheet. Lay meat on rack and let stand at room temperature for 1 hour.
Bring wine to a simmer over medium-high heat. Cook until reduced to 2 cups, about 15 minutes.
Tie parsley sprigs, thyme sprigs and bay leaves into a bouquet garni.
Pat beef dry and season generously with pepper. Tie each piece of meat with kitchen twine to keep it from falling apart.
Place oven rack in lower-middle position and preheat to 300°F.
Cook bacon in a large Dutch oven over medium-high heat, stirring occasionally, until crisp, 6-8 minutes. Using a slotted spoon, remove bacon to a paper-towel lined plate. Drain off all but 2 tbsp of bacon fat. Return Dutch oven to medium-high heat until fat begins to smoke. Add beef to pot and brown on all sides, 8-10 minutes total. Transfer beef to large plate and set aside.
Reduce heat to medium and add onion. Sauté onion 2-4 minutes until softened. Add garlic, flour and reserved bacon; cook, stirring constantly, until fragrant, about 30 seconds. Add reduced wine, broth and bouquet garni. Scrape bottom of pan to release fond. Return meat and any accumulated juices to pot. Increase heat to high and bring liquid to a simmer. Place a large piece of foil over pot and cover tightly with lid. Move pot into oven. Turn meat with tongs every hour, until dinner fork slips easily in and out of meat, 2 1/2 - 3 hours. Add carrots to pot after 2 hours of cooking.
Meanwhile, bring onions, butter, sugar and 1/2 cup water to boil in large skillet over medium-high heat. Reduce heat to medium, cover tightly and cook until onions are tender, 5-8 minutes. Uncover, increase heat to medium-high and cook until all liquid evaporates, 3-4 minutes. Add mushrooms and 1/4 tsp table salt; cook, stirring occasionally, until vegetables are browned and glazed, 8-12 minutes. Remove from heat and set aside.
Place 1/4 cup water in a small bowl and sprinkle gelatin powder over surface.
Transfer beef to cutting board when fully cooked; tent with foil. Allow braising liquid to settle for 5 minutes, then skim fat off surface with wide, shallow spoon. Remove bouquet garni and stir in onion-mushroom mixture. Bring liquid to simmer over medium-high heat and cook until mixture is slightly thickened and reduced to 3 1/4 cups, 20-30 minutes. Season sauce with salt and pepper. Add gelatin and stir until completely dissolved.
Remove kitchen twine and discard. Carve meat into 1/2-inch-thick slices against the grain. Divide meat among warmed bowls or transfer to platter. Arrange vegetables around meat, pour sauce on top, sprinkle with minced parsley and serve immediately.
*To prepare in advance:* follow recipe through step 10, but skip the gelatin step. Place the meat back in the sauce, cool to room temperature and refrigerate up to 2 days. Slice the beef and arrange in a 13x9" baking dish. Soften the gelatin, bring the sauce to a simmer and add the gelatin. Pour the warm sauce over the meat, cover with foil and bake at 350F until heated through, about 30 minutes.