1/2 cup salted butter, melted
2 tablespoons Dijon mustard
1 1/2 teaspoons kosher salt, divided
1 teaspoon black pepper, divided
2/3 cup panko (Japanese-style breadcrumbs)
1/2 cup crushed cornflakes cereal
2 ounces Parmesan cheese, grated (about 1/2 cup)
4 chicken breast cutlets (about 1 1/4 lb.)
3 1/2 tablespoons olive oil
3 garlic cloves, minced
1 teaspoon crushed red pepper
1 pound fresh broccoli florets (about 8 cups)
2 tablespoons salted butter
1 tablespoon all-purpose flour
1 cup whole milk
1 ounce grated Parmesan cheese (about 1/4 cup)
1 teaspoon fresh lemon juice
1/4 teaspoon kosher salt
1/4 teaspoon black pepper
Preheat oven to 400°F. Stir together butter, mustard, and 1/2 teaspoon each of the salt and black pepper in a medium bowl. Stir together panko, cornflakes, and Parmesan in a second shallow bowl. Dip chicken in butter mixture; dredge in panko mixture, pressing to adhere. Place on a baking sheet lined with aluminum foil. Bake in preheated oven until chicken is browned and done, about 17 minutes.
Meanwhile, stir together oil, garlic, crushed red pepper, and remaining 1 teaspoon salt and 1/2 teaspoon black pepper in a large bowl. Add broccoli, and toss to coat. Transfer to a rimmed baking sheet, and roast at 400°F until broccoli is browned and tender, about 17 minutes.
Melt butter in a 3-quart saucepan over medium-high. Whisk in all-purpose flour; cook, whisking constantly, 1 minute. Gradually whisk in whole milk. Bring to a boil, and cook, whisking constantly, until thickened, for 1 to 2 minutes. Whisk in grated Parmesan cheese, fresh lemon juice, salt, and black pepper. Serve immediately.