Warm about 1/2 cup of the Water (it should feel like warm bath water) and dissolve 1 teaspoon of the Sugar into it; sprinkle the Active Dry Yeast on top and let sit 5–10 minutes until foamy.
In a large bowl whisk together the Buckwheat Flour, All-Purpose Flour and a pinch of Salt so the dry ingredients are evenly combined.
Make a well in the center and add the foamy yeast, most of the warmed Milk (reserve a little to adjust batter if needed), and the beaten Eggs. Stir gently to form a smooth, slightly thick batter.
Stir in the melted Unsalted Butter to enrich the batter, then cover the bowl with a cloth and let it rest in a warm place for 45–60 minutes, until bubbly and slightly risen.
When the batter has risen, gently whisk it again; if it seems too thick, thin with a splash of reserved Milk or Water to a pourable but thick pancake batter consistency.
Heat a nonstick skillet or crepe pan over medium heat and brush lightly with Neutral Oil. Spoon a tablespoon or two of batter into the pan to make small, silver-dollar–size blini.
Cook until bubbles form on the surface and the edges look set, 1–2 minutes, then flip and cook the second side until golden, about 30–60 seconds. Repeat, adding more oil as needed and keeping finished blini warm on a plate covered with foil.
Serve the warm blini spread with a little sour cream and topped with bright Sour Cream and a spoonful of Salmon Roe; finish with a pat of unsalted butter if you like for extra richness.
