Step 3. Stir in mustard, garlic, Italian seasoning, salt, pepper, & red pepper flakes (if using). Simmer for 2-3 minutes and remove from heat. Add ⅔ cup of cheddar cheese, ¼ cup of parmesan cheese, and stir until well incorporated.
Step 6.After adding reserved pasta water to sauce, pour sauce over pasta & broccoli, and stir. In a small bowl, mix together the breadcrumbs along with the remaining cheddar and Parmesan cheese. Sprinkle mixture on top of pasta and cover with foil.