1 (3 1/2- to 4-pound) boneless beef chuck-eye roast, pulled into two pieces at natural seam and trimmed
1 1/2 pounds marrow bones
1 onion, quartered
1 celery rib, sliced thin
3 bay leaves
1 teaspoon black peppercorns
2/3 cup minced fresh parsley
1/4 cup Dijon mustard
1/4 cup minced fresh chives
3 tablespoons white wine vinegar
10 cornichons, minced
1 1/2 teaspoons pepper
1 pound small red potatoes, halved
6 carrots, halved crosswise, thick halves quartered lengthwise, thin halves halved lengthwise
1 pound asparagus, trimmed
Kosher salt and pepper
Flake sea salt
FOR THE MEAT: Adjust oven rack to lower-middle position and heat oven to 300 degrees. Season beef with 1 tablespoon salt. Using 3 pieces of kitchen twine per piece, tie each into loaf shape for even cooking. Place beef, bones, onion, celery, bay leaves, and peppercorns in Dutch oven. Add 4 cups cold water (water should come halfway up roasts). Bring to simmer over high heat. Partially cover pot and transfer to oven. Cook until beef is fully tender and sharp knife easily slips in and out of meat (meat will not be shreddable), 3 1/4 to 3 3/4 hours, flipping beef over halfway through cooking.
FOR THE PARSLEY SAUCE: While beef cooks, combine all ingredients in bowl. Cover and set aside.
Remove pot from oven and turn off oven. Transfer beef to large platter, cover tightly with aluminum foil, and return to oven to keep warm. Transfer bones to cutting board and use end of spoon to extract marrow. Mince marrow into paste and add 2 tablespoons to parsley sauce (reserve any remaining marrow for other applications). Using ladle or large spoon, skim fat from surface of broth and discard fat. Strain broth through fine-mesh strainer into large liquid measuring cup; add water to make 6 cups. Return broth to pot. (Meat can be returned to broth, cooled, and refrigerated for up to 2 days. Skim fat from cold broth, then gently reheat and proceed with recipe.)
FOR THE VEGETABLES: Add potatoes to broth and bring to simmer over high heat. Reduce heat to medium and simmer for 6 minutes. Add carrots and cook 10 minutes longer. Add asparagus and continue to cook until all vegetables are tender, 3 to 5 minutes longer.
Using slotted spoon, transfer vegetables to large bowl. Toss with 3 tablespoons parsley sauce and season with salt and pepper to taste. Season broth with salt to taste.
Transfer beef to cutting board, remove twine, and slice against grain 1/2 inch thick. Arrange servings of beef and vegetables in large, shallow bowls. Dollop beef with parsley sauce, drizzle with 1/3 cup broth, and sprinkle with flake sea salt. Serve, passing remaining parsley sauce and flake sea salt separately.
SERVES 6 TO 8
Marrow bones (also called soup bones) can be found in the freezer section or the meat counter at most supermarkets. Use small red potatoes measuring 1 to 2 inches in diameter.