Preparationfor coleslaw: Preheat oven to 425°F. Trim beet tops. Wrap each beet in foil. Roast until tender, about 1 1/2 hours. Cool in foil. Peel beets and grate coarsely. Blend oil, vinegar and horseradish in large bowl. Mix in beets, cabbage and onion. Season with salt and pepper. Cover; chill 2 days, tossing occasionally. for whitefish: Sprinkle whitefish with salt and pepper. Steam whitefish until opaque in center, about 10 minutes. Cool. Blend mayonnaise, horseradish and chopped tarragon in medium bowl. Flake fish coarsely; fold into dressing. Season with salt and pepper. Cover and chill 1 day to blend flavors. Drain half of coleslaw in sieve (reserve remainder for another use). Line eight 2/3-cup ramekins or custard cups with plastic wrap, leaving overhang. Pack 1/4 cup whitefish salad into 1 side of each ramekin; pack 1/4 cup drained coleslaw next to whitefish. (Can be made 4 hours ahead. Cover; chill.) Turn molds out onto plates; peel off plastic.
Preparationfor coleslaw: Preheat oven to 425°F. Trim beet tops. Wrap each beet in foil. Roast until tender, about 1 1/2 hours. Cool in foil. Peel beets and grate coarsely. Blend oil, vinegar and horseradish in large bowl. Mix in beets, cabbage and onion. Season with salt and pepper. Cover; chill 2 days, tossing occasionally. for whitefish: Sprinkle whitefish with salt and pepper. Steam whitefish until opaque in center, about 10 minutes. Cool. Blend mayonnaise, horseradish and chopped tarragon in medium bowl. Flake fish coarsely; fold into dressing. Season with salt and pepper. Cover and chill 1 day to blend flavors. Drain half of coleslaw in sieve (reserve remainder for another use). Line eight 2/3-cup ramekins or custard cups with plastic wrap, leaving overhang. Pack 1/4 cup whitefish salad into 1 side of each ramekin; pack 1/4 cup drained coleslaw next to whitefish. (Can be made 4 hours ahead. Cover; chill.) Turn molds out onto plates; peel off plastic.