Preheat oven to 400°F. Line a rimmed baking sheet with parchment paper.
Using a serrated bread knife in a gentle sawing motion, cut 12 (4x2-inch) rectangles from bread slices. Arrange bread rectangles in a single layer on prepared baking sheet.
In a medium bowl, stir together fish, ½ cup cheese, cream, mayonnaise, chives, horseradish, and black pepper. Spread 1 tablespoon fish mixture onto each bread rectangle.
Bake until fish mixture begins to brown and bread is toasted, 7 to 9 minutes. Sprinkle with remaining ¼ cup cheese. Serve warm or at room temperature within an hour.
Just before serving, garnish with minced chives and cracked black pepper, if desired.
Recipe by TeaTime Magazine at https://teatimemagazine.com/smoked-fish-toasts/