While whisking constantly, slowly pour in 1 cup low-sodium chicken broth and keep whisking until smooth. Bring to a boil over high heat. Reduce the heat to maintain a simmer and cook, stirring occasionally, until slightly thickened enough to coat the back of a spoon, 2 to 3 minutes. Season with1/4 teaspoon kosher salt and a few grinds of black pepper. Taste and season with more kosher salt as needed.