Combine eggs, milk, flours, maple syrup, lemon zest, and salt in a blender. Pulse until combined. Alternatively, whip with a whisk in a bowl until the batter is smooth.
On the stove top, melt 1 tablespoon butter in a 8″ cast iron (well seasoned) skillet. Swirl around to cover the pan once melted. Turn off the heat, add the batter to the pan, and transfer the pan to the hot oven. Bake, without opening the oven door, in oven until golden brown and puffed, 20-25 minutes.
Slice apples in to 1/4" thick slices. Place in a pot/pant with maple syrup, butter, and cinnamon. Heat oven medium-low heat until apple are starting to soften, 8 to 10 minutes.
Remove dutch baby from oven and top with apples. Serve with butter and extra maple syrup if desired.
Tips + Tricks: You could easily use 100% whole wheat flour with the dutch baby. I'd recommend using the white wheat or switching to a pastry (soft) wheat flour.