In a bowl, combine the four and salt and set aside.
Blend the eggs and sugar in a food processor then add milk and water. Gradually add flour and pulse until smooth. Combine the bicarb with the lemon juice and add to the mixture, along with the vegetable oil. Allow to rest for 10 minutes.
Heat a small frying pan over high heat. Brush with oil then add the mixture by the spoonful to make blinis. Flip once bubbles appear and cook for another minute on the other side. Remove from the pan and allow to cool.
Spread a little butter on each and top with 1 teaspoon of caviar. Fold into triangles and serve.