01 - Bring a large pot of salted water to a boil, add pasta, and cook until al dente. Drain thoroughly and set aside.
02 - In a medium saucepan, whisk together Dijon mustard, maple syrup, and heavy cream. Warm over medium-low heat, then add shredded cheddar and whisk continuously until cheese melts and the sauce is smooth. Season with salt and pepper to taste.
03 - In a large mixing bowl, toss the cooked pasta with chicken, broccoli florets, and the warm maple mustard sauce until evenly coated.
04 - In a small bowl, combine panko breadcrumbs with melted butter and Parmesan if using. Stir until evenly moistened, then sprinkle mixture uniformly over the pasta in a greased baking dish.
05 - Place baking dish in a preheated oven at 375°F and bake for 20 to 25 minutes, or until the top is golden and the casserole is bubbling at the edges.