Remove head, tail, fins, and the skin surrounding them.
Sprinkle 1/2 teaspoon salt inside fish.
Wrap in large sheet of wax paper, with folded seam at top.
Place on microwave-proof trivet in a baking dish.
Cook for 3 minutes.
Rotate the dish half a turn.
Cook another 3 minutes.
Do not remove covering.
Then let stand for 3 minutes.
In an ovenproof casserole heat butter for 15 seconds.
Add walnut meats, and cook for 3 minutes, stirring at 1 minute intervals.
Combine the sour cream, lemon juice, horseradish, and salt with any liquid that has formed from the cooked fish (but no more than 1/2 cup).
Combine this mixture with the walnuts in the casserole and heat 30 seconds.
Serve with the bass.