In a stockpot, combine chicken broth, onion, cauliflower, and broccoli. Bring to a boil and reduce heat to low. Continue to simmer until vegetables are tender. Season with curry powder, chicken bouillon, salt, and pepper.
In a bowl, combine flour and 1/2 cup of the milk. Whisk briskly until there are no lumps. Add mixture to soup, stirring continuously as soup thickens. Stir in Cheddar cheese until completely melted.