Here's an odd one that tastes GREAT...
Melt a stick of butter in a microwave. Add cream-style horseradish (no pulp, the creamy stuff for prime rib). My favorite is Beaver brand, labelled "especially for prime rib" with the white color-coded lid. It takes about 1/3 of the small jars to mix into a buttery hollandaise consistency. I add a touch of garlic and dill weed, and as with all my seafood I add Chef Prudhomme's Seafood Magic (not cajun) to add a tint of red and distinct finished flavor to the sauce.
Using a hinged fish grilling basket (the big rectangular kind, not the pu-pu fish shaped ones big enough for a kibbie
) baste the fillet on the non-skin side with the sauce (both sides if skinned) and broil over moderately high heat until the edges are crisp and brown, yet the sauce has broiled on to the fillet with a sort of glazed sauce look.
Use the rest of the sauce as a butter - tart sauce with the cooked fillet.
(Special thanks to Roger Johnson of Bellevue Washington)