Preheat the fryer to 375 degrees F.
In a mixing bowl, whisk
together the flour, cornstarch, egg
, and seltzer water
. Mix well to make a smooth batter
. Season with salt and cayenne. Dip each floret into the batter, shaking off any excess. Carefully add the battered broccoli to the oil and fry
until crispy, about 2 to 3 minutes. Remove and drain
on paper towels. Season with salt.