Place a 9-inch cast-iron skillet or an ovenproof skillet in the middle rack of the oven and preheat it to 200℃ for at least 20 minutes.
Add the batter ingredients (milk, eggs, vanilla, zest, flour, sugar and salt) into a blender and blend until super smooth. Set this aside to rest while the pan preheats and you can prep the apples, cinnamon sugar and labneh mix.
Carefully remove the skillet from the oven and add the butter to it. Swirl it all around a few times until the butter melts completely and coats all the sides of the pan up.
Pour the batter immediately and scatter the sliced apples over the top avoiding the edges. Sprinkle the cinnamon sugar all over the apple slices.
Place the skillet carefully back in the oven and bake for 20 to 25 minutes without opening the oven door until the Dutch baby is puffed, lightly browned across the top, and darker brown on the sides and edges.
Meanwhile, prepare your cinnamon sugar by mixing sugar and ground cinnamon. Also prepare the sweetened labneh by whisking labneh with honey.
Remove from oven, slice into wedges and serve immediately with labneh (Greek yoghurt), berries, or any syrup. You may dust with powdered sugar before serving if preferred.
