How to Make It
In a bowl, combine the water, yeast and sugar and let stand for 5 minutes. Whisk in the 1 1/2 cups of milk and the egg. Add both flours and the salt and whisk until smooth, then whisk in the 4 tablespoons of melted butter. Cover and let stand for 30 minutes.
Set a 10-inch nonstick skillet over moderate heat and brush with butter. Pour in a scant 1/3 cup of the batter and swirl to coat the pan. Cook the blini until tiny bubbles form on the surface and the bottom is browned, 2 minutes. Carefully flip the blini and cook until the bottom is lightly browned in spots, 30 seconds. Transfer to a baking sheet. Repeat with the remaining batter, buttering the pan and whisking in 1 or 2 tablespoons of milk to thin the batter as needed. You should have about 13 blini. Let cool slightly.
In a bowl, using a handheld electric mixer, beat the crème fraîche until stiff. Spread a thin layer of crème fraîche on 8 or 9 blini and stack them; top with a plain blini. Trim off the rounded edges of the stack and cut into 1-inch squares. Dip a layered side of each square into the chives and set them on a platter. Dollop caviar on top and serve.