Whisk together first 5 ingredients in a large bowl.
Heat milk and butter in a saucepan over low heat; stir until butter melts and thermometer registers 110°. Pour warm milk mixture into flour mixture, and whisk until smooth. Cover with plastic wrap, and let rise in a warm place, free from drafts, until doubled in volume (1 to 1 1/2 hours).
Whisk buckwheat batter to deflate; whisk in eggs.
Heat griddle or large skillet over medium heat, and brush lightly with melted butter. Working in batches, spoon 1 tablespoon batter onto griddle, spacing at least 2 inches apart. Cook until bubbles form on top and begin to pop, about 1 to 2 minutes. Turn blini; cook 1 minute or until golden brown on bottom. Cover with foil, and keep warm while cooking remaining blini.