In a bowl, beat the softened butter with both varieties of mustard, lemon zest and 1 tbsp of the dill. Season with salt and pepper. This can be refrigerated overnight, however let soften before using.
Bits and Pieces
Preheat the broiler with the rack 6 inches from the heat. Spread the baguette slices on a rimmed baking sheet and broil until golden brown and crisp, about 1 1/2 minutes per side. Let cool.
Spread each toasted baguette slice with mustard butter, top with smoked fish and arrange on a platter. Sprinkle with the remaining dill and serve.