How to Make It
In a large pot, heat 3 inches of vegetable oil to 350°. In a medium bowl, whisk 1 cup of the flour with the cornstarch, baking powder, 1 teaspoon of kosher salt and a pinch of black pepper. Whisk in the club soda to make a thin batter. Let the batter stand for 5 minutes.
Place the remaining 1 1/2 cups of flour in a bowl. Season the shrimp, cod, squid, fennel and lemon slices with salt and black pepper. Dust with the flour. Dip them in the batter in batches, scraping some of the excess against the side of the bowl, and fry them in batches in the hot oil until lightly golden and crisp, about 4 minutes. Drain the fritto misto on paper towels and sprinkle with salt. Transfer to a large plate, sprinkle with the parsley and serve with lemon wedges.