Potato rosti with smoked salmon, egg and hollandaise

Name: Potato rosti with smoked salmon, egg and hollandaise
Prep time: 25 min
Cook time: 20 min
Total time: 45 min
Cuisine: European, British
Ingredients: 3 medium potatoes (desiree or Pontiac); 2 tablespoons horseradish cream; 1 tablespoon plain flour; 4 very fresh eggs; 50g butter; 1 tablespoon olive oil; 4 slices smoked salmon; 2 tablespoons finely chopped chives, to garnish; Hollandaise and rocket, to serve