Preheat oven to 425°F. Whisk flour, sugar,
salt, pepper and Parmesan in a bowl. (This can be made the day before and refrigerated,
simply whisk gently to combine when ready to cook).
Blend eggs and milk until well combined and
frothy. Add the flour mixture and stir well so there are no dry patches of
flour.
Heat a 9-10" cast iron pan over
medium-high heat. When hot, melt the butter to coat the pan. Pour the pancake
batter into the pan, then transfer into the oven and bake until puffed and
golden, 12-15 minutes.
Remove from the oven, and layer smoked salmon, crème fraîche and arugula over the top. Serve hot.