Pour enough oil into a deep pan to fill the pan a little less than halfway. Be sure to use a pan into which you can insert a large basket, or strainer with a handle, for frying. Heat the oil over medium-high heat until just smoking. If you have a high temperature thermometer, the temperature of the oil throughout the frying process should remain at about 360 to 375 degrees F.
In a wide, shallow bowl, mix 1/2 the calamari, 1/2 the lemon slices, and 1/2 the scallops. Sprinkle the mixture with 1 cup cornstarch and salt and, using your hands, toss the mixture quickly so that the cornstarch coats everything. Toss the coated mixture into the basket (or large strainer) with a handle. Bat the strainer against your hand to shake off any excess cornstarch.
Carefully drop the coated seafood and lemon mixture into the hot oil and cook until golden brown and crispy, about 1 minute. Remove the fritto to a plate lined with paper towels to drain. Immediately repeat, combining the remaining lemons, calamari, scallops, and cornstarch.
Season the hot fried foods with salt and pepper and serve immediately with fresh lemon wedges.
Recipe courtesy of Mario Batali