1) Preheat grill to medium-high heat. Wash broccoli heads well with Fruit & Vegetable Wash, rinse with water and then cut into florets. Toss broccoli florets with olive oil, salt, and pepper.
2) Add broccoli florets to a grill pan and grill for 5-6 minutes total, stirring a few times, until broccoli is tender, but charred in spots. Remove broccoli before it gets completely mushy.
3) Meanwhile, make cheese sauce while melted butter in a medium pot. Whisk in flour and cook for a minute or two until the mixture turns a light tan color. Slowly whisk in milk. Turn heat down to low. Add cheese and stir to combine. Continue to stir while the sauce thickens and cheese melts. Season sauce with a pinch of salt and dried mustard (optional).
Serve grilled broccoli with cheese sauce on the side or drizzle the cheese sauce over the broccoli.