In the work bowl of a food processor, combine salmon, cream cheese, sour cream, horseradish root, and white pepper. Pulse until well blended and smooth. Transfer mixture to a covered container, and refrigerate until cold, approximately 4 hours.
Just before serving, let mixture soften briefly at room temperature for ease of piping. Transfer mixture to a piping bag fitted with a large open-star tip (Wilton #1M), and pipe onto toasts in an upright fashion.
Serve immediately.
Recipe by TeaTime Magazine at https://teatimemagazine.com/salmon-petits-toasts-recipe/