Place milk and 3 tablespoons butter in small saucepan. Stir over low heat just until butter melts. Meanwhile, whisk together both flours, sugar, salt, and yeast in a medium bowl. Pour warm milk mixture into dry ingredients and whisk until smooth. Cover with plastic wrap and let rest at room temperature until doubled in volume, 1½–1¾ hours.
After resting, batter will be bubbly and lofty. Whisk to deflate; then stir in beaten eggs just to incorporate—the texture should be silky. Meanwhile, set a skillet over medium heat and add a tablespoon of butter. Working in batches, pour 2 tablespoons batter for each blini onto skillet, spacing apart. Cook until bubbles form on top and they begin to pop, about 1½ minutes. Turn blinis; cook until golden brown on bottom, another 1½ minutes (add more butter to the pan as you need it). Transfer blinis to a serving platter. Tent with foil to keep warm while you cook remaining blinis. Makes approximately 12 blinis.
Assembly: Serve blinis with a dollop of crème fraîche, smoked salmon, and caviar—the more the better!