Preheat your waffle iron. If you want to hold the finished waffles until serving time, preheat your oven to 200 degrees.
Melt the butter and reserve. In a large bowl, whisk together the flour, baking powder, salt, and pepper. In another bowl, whisk together the milk and eggs until well blended. Pour the liquid ingredients over the dry ingredients and whisk gently to combine. Fold in the salmon, onion, dill, and melted butter.
Lightly butter or spray the grids or your iron, if needed. Brush or spray the grids again only if subsequent waffles stick.
Spoon out 1/2 cup of the batter (or the amount recommended by your waffle maker's instructions) onto the hot iron. Spread the batter evenly over the grids with a metal spatula or wooden spoon, stopping right before the edge. Close the lid and bake until golden and crisp. Serve immediately or keep the waffles, in a single layer, on a rack in the preheated oven while you make the rest of the batch.
Serve with either a scoop of cream cheese and a sprinkling of chopped scallions, or a generous spoonful of creme fraiche (or sour cream) and some salmon caviar.
Recipe adapted from Waffles: From Morning to Midnight