Parchment paper provides a nonreactive barrier between the cola-based braising liquid and the aluminum foil.
1 (3 1/2-pound) beef brisket, flat cut, fat trimmed to 1/4 inch
Salt and pepper
4 teaspoons vegetable oil
1 pound onions, halved and sliced 1/2 inch thick
2 cups cola
1 1/2 cups ketchup
4 teaspoons onion powder
2 teaspoons packed dark brown sugar
1 teaspoon garlic powder
1 teaspoon dried thyme
1. Using fork, poke holes all over brisket. Rub entire surface of brisket with 1 tablespoon salt. Wrap brisket in plastic wrap and refrigerate for at least 6 or up to 24 hours.
2. Adjust oven rack to lower-middle position and heat oven to 325 degrees. Pat brisket dry with paper towels and season with pepper. Heat 2 teaspoons oil in 12-inch nonstick skillet over medium-high heat until just smoking. Place brisket fat side down in skillet; weigh down brisket with heavy Dutch oven or cast-iron skillet and cook until well browned, about 4 minutes. Remove Dutch oven, flip brisket, and replace Dutch oven on top of brisket; cook on second side until well browned, about 4 minutes longer. Transfer brisket to plate.
3. Heat remaining 2 teaspoons oil in now-empty skillet over medium heat until shimmering. Add onions and cook, stirring occasionally, until soft and golden brown, 10 to 12 minutes. Transfer onions to 13 by 9-inch baking dish and spread into even layer.
4. Combine cola, ketchup, onion powder, sugar, garlic powder, thyme, 1 teaspoon salt, and 1 teaspoon pepper in bowl. Place brisket fat side up on top of onions and pour cola mixture over brisket. Place parchment paper over brisket and cover dish tightly with aluminum foil. Bake until tender and fork easily slips in and out of meat, 3½ to 4 hours. Let brisket rest in liquid, uncovered, for 30 minutes.
5. Transfer brisket to carving board. Skim any fat from top of sauce with large spoon. Slice brisket against grain into ¼-inch-thick slices and return to baking dish. Serve brisket with sauce.
TO MAKE AHEAD: Follow recipe through step 4. Allow brisket to cool in sauce, cover, and refrigerate overnight or up to 24 hours. To serve, slice brisket, return to sauce, and cover with parchment paper. Cover baking dish with aluminum foil and cook in 350-degree oven until heated through, about 1 hour.
GETTING A GREAT SEAR
Brisket is a flat cut of meat that curls up when you try to sear it. We fixed this problem with an unlikely tool: a Dutch oven. Weighing down the brisket with a heavy Dutch oven (the foil makes cleanup easier) ensures a more even, more thorough sear.