Mix buckwheat flour, baking powder, salt, pepper, and milk into a smooth batter.
Stir in the mustard powder, grated cheddar, and chopped chives.
Whisk egg whites with salt in a separate bowl until soft peaks form.
Fold the whisked egg whites gently into the buckwheat batter using a metal spoon.
Melt butter in a frying pan and spoon in batter to form 10cm pancakes.
Fry blinis for 2-3 minutes per side until golden-brown and keep them warm.
Repeat the frying process until all the batter mixture is used.
Whisk eggs and yolks in a bowl and season with salt and pepper.
Melt butter in a saucepan, add eggs, and cook while stirring for 2 minutes.
Serve blinis topped with eggs, chives, smoked salmon, and lemon wedges.