Rinse and cut the salmon into 20 very thin slices.
For the pancakes: Preheat a griddle over medium-high heat. Mix the buckwheat flour, all-purpose flour, baking powder and salt. Add 1 cup cold water and mix until you have a thick dough. Add 2 cups hot water and mix until you get the consistency of a pancake batter. Pour about 1 cup of the batter on the griddle. Cook the pancake on one side for 3 to 4 minutes, do not flip it, you need to have a crispy side and a tender side. Remove from the griddle when cooked through and repeat for the remaining batter. Keep the pancakes hot in a warm oven until ready to serve.
For the gravlax ploye: Spread a generous amount of cream cheese on each hot pancake. Add 2 slices of the salmon. Mix the fennel in a bowl with the capers and some caviar if using, then lay the salad on top of the salmon. Add a slice of egg to each pancake, then serve.