Mix both flours and salt in a large bowl. Melt butter in pieces in a small pot. Pour in milk and warm it up lukewarm, remove from the stove. Crumble yeast into the butter-milk and dissolve it while stirring. Add the yeast milk and eggs to the flour and work into a smooth dough with the dough hooks of the hand mixer. Cover and allow to rise for about 45 minutes.
In the meantime cut half of the cucumber into slices. Cut the rest in half lengthwise, remove the seeds with a ball cutter. Finely dice the flesh. Peel and finely dice the onion. Wash the dill, dab dry and pluck off the little flags. Finely chop all but a few flags for garnishing. Mix sour cream, dill, cucumber cubes, lime juice and lime zest. Season to taste with salt, pepper and 1 pinch of sugar
Stir the dough properly with a wooden spoon. Heat the heart-shaped waffle iron (21 cm Ø) and grease it lightly. Bake 4 waffles from the dough one after the other. Divide the waffles into individual hearts. Cover the waffle hearts with smoked salmon, cucumber slices and cucumber-dill sour cream and mix with the remaining dill garnish.