In a large bowl, whisk together flour, sugar, baking powder, salt, and pepper. Whisk in egg yolk, seltzer, milk, melted butter, and dill. Batter will be lumpy.
In a medium bowl, beat egg whites with a whisk or hand mixer until they form stiff, but not dry, peaks. Fold egg whites into the waffle batter just until streaks disappear. Let batter stand while waffle iron is heating.
Preheat oven to 150-200 degrees F (or set to the "warming" setting).
Preheat and grease your waffle iron according to manufacturer's directions. Cook waffles until golden brown and crisp, adjusting settings to your unit's specifications.* Transfer waffles in a single layer to a wire rack-lined baking sheet and place in the pre-heated oven to keep warm.
POACH THE EGGS
Fill a large bowl with hot (not boiling) water and cover to keep warm. Set aside.
Fill a 10-12 inch diameter, straight-sided pan with about 2 inches of water. Stir in vinegar. Bring to a full boil, then reduce heat until the water is just barely simmering.
Crack an egg into a dry measuring cup and gently lower the egg into the water. Repeat with remaining eggs, leaving room between them in the pan and allowing each white to coagulate slightly before adding the next egg. Use a slotted spoon to gently move eggs in the pan a few times so they don't stick to the bottom.
Cook for 3-4 minutes, until your desired doneness is reached. Transfer eggs to the bowl of hot water while you make the hollandaise (see "Essentials" link in ingredients).
Place 2 slices of smoked salmon on top of a warm waffle. Remove eggs from the warm water with a slotted spoon and drain on a paper towel. Top the salmon with an egg and a small ladleful of hollandaise. Garnish with dill. Serve immediately.
If doubling for a crowd, the restaurant trick of par-poaching eggs works well. The night before, poach the eggs to about 30 seconds less than your desired doneness and transfer them to a bowl of ice water. Cover with plastic wrap and refrigerate. When ready to serve, return the eggs to a pan of barely simmering water for 30-60 seconds, until warmed to your preferences.*Number of waffles will vary by model; I get 4-5, 4-inch square Belgian-style waffles per batch.