Cut vegetables into florets (you should end up with roughly 8 cups of broccoli and 4 cups of cauliflower). Bring 8 cups of salted water to a boil. Add cauliflower and boil for 2 minutes. Add broccoli and boil for 6 more minutes. Drain.
Melt butter and flour in a saucepan. Add milk, and bring to a boil. Remove from heat and stir in remaining ingredients. Place vegetables in larg dish, and top with sauce.