Cut the potatoes into small cubes and boil for eight minutes. Drain, cool and push through a fine metal sieve to mash.
Mix well with the flour, soda, yoghurt and a pinch of salt and put into a piping bag.
Stir the horseradish into the creme fraiche and season with a little salt and pepper. Set aside.
Heat a sauté pan with the oil and pipe in small amounts of the batter. Cook until bubbling on the top and carefully flip over. Cook the other side until golden and put on a plate lined with kitchen towel. Repeat until you have used the batter.
Top each blini with a teaspoon of the horseradish mixture, and a little smoked salmon. Add the keta to each and serve with sliced spring onion and lemon zest if you like.
400g purple potatoes (or maris piper) cooked, cooled and mashed
8tbsp plain flour
1tsp bicarbonate of soda
4tbsp low-fat natural Greek style yoghurt
1tbsp rapeseed oil
100ml light creme fraiche
40g grated horseradish
200g smoked salmon, sliced
10tsp salmon caviar (Keta)
Salt and pepper