Wash the cucumber thoroughly, rub dry and slice lengthwise into slices about 2 mm thick. Evenly cover the cucumber slices with smoked salmon, carefully roll up and pin with wooden toothpicks. For the sauce, mix crème fraîche with the freshly grated horseradish and the cream. Season to taste with salt and pepper. Serve the rolls with the sauce. Finally, drizzle with a little olive oil, garnish with dill tips and season with salt and pepper.