Fill a large deep pot with 1 inch water, and place cauliflower in the pot. Cover and simmer until cauliflower is tender, about 15 minutes or until a paring knife slides easily into the cauliflower.
Make sauce by melting butter in saucepan over medium heat. Add flour and stir for one minute. Add milk and and stir until mixture is slightly thickened. Add cheese and stir until melted.
When the cauliflower is melted, pour sauce generously over the top and scatter scallions over the top. Serve with extra sauce in a pitcher.
Keywords: vegetarian cauliflower with blue cheese sauce