Remove the zest of the lemon with a vegetable peeler in fat strips and toss it in a bowl. Add the salt, sugar, white peppercorns, and dill; rub all the ingredients together with your hands to release the oils in the zest and dill. Lay the fish out on a large sheet pan or glass baking dish. Pack the salt mixture on top of and around the salmon. Cover with another sheet pan and place a brick or heavy can weight on top to press out the moisture from the salmon. Refrigerate for 24 to 36 hours to cure the fish. Scrape the salt mixture off the salmon and lightly rinse the fish under cool water; pat dry with paper towels. The cured salmon will be firm but pliable.
To set up the presentation, lay the salmon on a large wooden cutting board. (The whole fish looks great as a center piece on the table, so only slice a quarter of the gravlax at a time.) With a very sharp knife slice the salmon New York Deli-style; paper-thin on a slight angle. Serve the cured salmon with the blini, the dill creme fraiche, and radish-lime salsa on the side. This is an interactive hors d'oeuvre: let your friends attack it, then slice more as needed.
To prepare the blini, in a large bowl, proof the yeast in the warm milk for 10 minutes, stirring to dissolve. In another large bowl, sift the all-purpose flour, buckwheat flour, salt, and sugar together. Make a well in the center and pour in the yeast mixture, melted butter, and egg yolks (reserve the whites) and whisk until smooth. Cover with a towel and let it rise in a warm place for 1 1/2 hours.
Just before you are ready to cook the blini, beat the egg whites until stiff, then fold them into the batter. Place a griddle or non-stick skillet over medium-high heat and brush it with a little melted butter. Pour 1 tablespoon of the batter into the pan, to make pancakes about 3 inches in diameter. Cook for about 30 seconds, then flip them over with a spatula and cook another 30 seconds. Stack the blini on a platter and wrap them in a cloth napkin to keep them warm.
Dill Creme Fraiche:
Mix all ingredients together in a bowl until combined.
Yield: 3/4 cup
Put all the salsa ingredients in a food processor and pulse 5 times to combine. Put it in a bowl and serve.