Preheat oven to 400°F. Cook pasta to al dente according to package directions. During last minute of cooking, add broccoli. Drain well; set aside.
Meanwhile, melt butter in large saucepan over medium heat. Add flour, salt, pepper, mustard, cayenne and nutmeg. Whisk one minute. Whisk in milk and bring to boil. Reduce heat to medium-low; simmer until sauce thickens and coats back of spoon. Whisk in cheeses. Add Worcestershire sauce. Season generously with salt and pepper.
Add pasta and broccoli and toss to coat. Pour into buttered 9×13-inch casserole dish. In small bowl, combine panko, parmesan and butter. Sprinkle over macaroni and cheese.
Bake 15 to 20 minutes or until top is golden and bubbly. Garnish with chives and serve.