Once the roast is tender, transfer it to a sheet pan and set aside.
Place a fine-mesh sieve over a large bowl and strain the cooking liquid, discarding the herbs and garlic. Return the strained liquid to the pot over medium heat.
In a small bowl, whisk together 1/4 cup beef broth and 3 tablespoons flour until a thin paste forms. This will thicken your gravy.
While whisking, slowly pour the slurry into the pot, stirring continuously. Simmer, whisking frequently, until the gravy thickens, 5 to 8 minutes. Taste and adjust seasoning with salt and pepper as needed. Reduce heat to low, cover, and keep warm.