Position rack in upper third of oven; preheat broiler. Combine 1 pound ground beef and the chopped onion in a large broiler-safe skillet; cook over medium heat, breaking the beef into bite-size pieces with a wooden spoon, until the beef is no longer pink, about 10 minutes. Add chopped broccoli; cook, stirring occasionally, until tender-crisp, about 5 minutes. Add 3 tablespoons flour, 1½ tablespoons minced garlic and 1 tablespoon sage; cook, stirring constantly, until the mixture is well coated, about 1 minute.
Add 1½ cups milk; bring to a lively simmer over medium-high heat. Cook, stirring constantly, until thickened, about 2 minutes. Stir in 4 ounces cream cheese and 1 cup Cheddar until melted, about 1 minute. Remove from heat and stir in 2 teaspoons garlic-and-herb seasoning, ½ teaspoon salt and ¼ teaspoon pepper.
In a small bowl, combine ½ cup panko, 1 tablespoon oil, ½ teaspoon paprika and the remaining ½ teaspoon garlic-and-herb seasoning. Sprinkle evenly over the mixture in the skillet.
Broil until the panko is golden brown and the edges are bubbling, 1 to 3 minutes.
