Makes 20:
400g purple potatoes (or Maris Piper), cut into small cubes
8 tablespoons plain flour
1 teaspoon bicarbonate of soda
4 tablespoon low-fat natural Greek style yogurt
Salt
100ml light créme fraîche
40g grated horseradish
1 tablespoon rapeseed oil
200g smoked salmon, sliced
1 teaspoon salmon caviar (Keta)
Finely sliced spring onions and lemon zest, to garnish