(If planning to serve as soon as they’re done), preheat oven to 250 degrees. Have a baking sheet lined with paper towels ready. Trim ends off zucchini and grate them either on the large holes of a box grater or, if you have one, using the shredding blade of a food processor.
In a large bowl, toss zucchini with 1 teaspoon coarse salt and set aside for 10 minutes. Wring out the zucchini in one of the following ways: pressing it against the holes of a colander with a wooden spoon to extract the water, squeezing out small handfuls at a time, or wrapping it up in a clean dishtowel or piece of cheese cloth and wringing away.
Return deflated mass of zucchini shreds to bowl. Taste and if you think it could benefit from more salt add a little bit more. Stir in onion, egg, flour and some freshly ground black pepper.
In a large heavy skillet, heat 2-3 tablespoons of oil over medium-high heat until shimmering. Drop small bunches of the zucchini mixture onto the skillet only a few at a time so they don’t become crowded and lightly nudge them flatter with the back of your spatula.
Cook the fritters over moderately high heat until the edges underneath are golden, about 3 to 4 minutes.
Flip the fritters and fry them on the other side until browned underneath again, about 2 to 3 minutes more. Drain briefly on paper towels then transfer to baking sheet and then into the warm oven until needed. Repeat process, keeping the pan well-oiled, with remaining batter.
Cook’s Note: I like to make sure that the fritters have at least 10 minutes in the oven to finish setting and getting extra crisp.
Do ahead: (This is the best part!)These fritters keep well, either chilled in the fridge for the better part of a week and or frozen in a well-sealed package for months. When you’re ready to use them, simply spread them out on a tray in a 325 degree oven until they’re hot and crisp again.