Place milk and butter in small saucepan. Stir over low heat until butter melts and thermometer registers 110°F (if mixture gets too warm, cool until temperature returns to 110°F).
Pour warm milk mixture into flour mixture and whisk until smooth. Cover with plastic wrap and let stand in warm draft-free area until doubled in volume, 1 to 1 1/2 hours.
Whisk buckwheat batter to deflate; then whisk in eggs. Do ahead Can be prepared 1 day ahead.
Transfer to large bowl. Cover; chill (may increase in volume; rewhisk before using).
Preheat oven to 200°F.
Heat griddle or large skillet over medium heat.
Brush lightly with melted butter. Working in batches, pour 2 tablespoons batter for each blini onto griddle, spacing apart. Cook until bubbles form on top and begin to pop, about 1 1/2 minutes. Turn blinis; cook until golden brown on bottom, about 1 1/2 minutes.
Transfer to baking sheet. Tent with foil and place in oven to keep warm while cooking remaining blinis. Do ahead Blinis can be made 1 day ahead. Cool, cover, and chill.
Brush blinis lightly with melted butter and rewarm on baking sheet in 350°F oven 5 minutes.
Arrange warm blinis on platter. Spoon 1 rounded teaspoon crème fraîche atop each. Top with smoked salmon.
Garnish with salmon roe and dill sprigs and serve.
