Place the rice, onions, stock, and saffron in a medium-size saucepan and bring to a boil.
Let boil for 2 to 3 minutes, then cover and reduce heat to lowest point.
Cook for 45 minutes, then turn off heat and let stand 10 minutes more.
Steam the cauliflower until tender, about 15 to 18 minutes.
Place in a blender with the milk and process on medium speed until smooth.
Stir in the cheese with a spatula, then process again on medium speed until the cheese is incorporated into the sauce.
Place the hot rice in the bottom of a 10-inch quiche plate.
Arrange the haddock on top, then spread the cauliflower mixture in a thin layer over the entire casserole.
Sprinkle with the paprika and bake at 350° for 30 minutes.
Sprinkle with the parsley, if desired.