Stir together yogurt and ricotta cheese. Scrape mixture into a fine mesh sieve lined with a coffee filter. Set sieve over a bowl and cover with plastic. Refrigerate overnight or up to 2 days.
Skillet Flatbread: In a large bowl, whisk together flour, salt and baking powder. Make a well in the centre of the flour mixture. Add yogurt, egg and melted butter. Using a fork, whisk together and slowly start stirring in the flour until a soft sticky dough forms.
Dump out dough onto a floured work surface and knead gently for about 2 minutes until smooth dough forms. Cover lightly and let rest for 15 minutes. Divide dough into 8 pieces and roll each piece into an 7 inch (17.5 cm) circle. Roll up into a cylinder and make into a coil. Repeat with all the dough. Let rest for 15 minutes.
Using a rolling pin, roll out dough into a thin round about 6 inches (15 cm). Place a large nonstick skillet over medium low heat and melt some of the cubed butter. Place 2 pieces of dough in pan and cook for about 4 minutes or until deep golden brown. Turn over and cook for another 3 minutes or until golden brown. Repeat with remaining butter and dough.
(Make-ahead: Let cool, wrap in foil and refrigerate for up to 3 days. Warm in 300 F (160 C) oven in foil for about 15 minutes.)
Stir dill, garlic, salt and pepper into labneh and spread over skillet flatbread. Sprinkle with smoked trout and radishes to serve. Garnish with dill springs and cut into wedges to serve.