Whisk together the flours, yeast and salt. Mix in the milk and stir until smooth. Cover and set aside until it has doubled in size.
Separate the egg. Mix in the yolk to the pancake mixture. Whisk the egg white until stiff then fold into the batter. Cover and set aside another 15 minutes or so.
Warm a large skillet/frying pan over a medium heat and brush with a little vegetable oil or butter. Put around 4-5 spoonfuls into the skillet at a time with space between them. Once the pancakes start to bubble in a few places, flip them over and cook another couple minutes on the other side. Keep warm until ready to use (eg wrap in a dish towel then in foil or put in a low over, covered), and repeat with the rest of the batter.
Top each blini with one or two small pieces of smoked salmon or gravlax and a small spoonful (around ½ tsp) of sour cream (or other toppings, as you prefer) then serve.
Notes
If you would like to make gravlax for these, try this gravlax recipe.