Put all the ingredients in a bowl and whisk well with an electric hand mixer until the cream thickens and becomes light and airy.
Season to taste with salt and freshly ground pepper, and a little more horseradish if you like. *Use a piece of fresh horseradish and grate it yourself – it makes the best horseradish cream.
Keep the cream in the fridge until you are ready to assemble the canapés - it keeps well for 2-3 days in the fridge.
Rösti waffles with smoked salmon and horseradish cream
Place the thawed rösti in a hot waffle iron and press them flat. Cook until golden and crisp.Continue until all the rösti are done, transferring them to a wire rack as you go so they stay crisp. Let them cool so the cream doesn't melt.
Spread a little horseradish cream over the base of each rösti and lay a piece of smoked salmon on top. Pipe or dot a few more small mounds of horseradish cream on top and garnish with watercress or dill.I keep the cream in a piping bag, which makes it easy to top the salmon neatly.
Season with freshly ground pepper just before serving.