Fill a heavy-bottomed pot with about 1½ inches of vegetable oil and heat it to 340°F (170°C). Prepare a wire rack lined with paper towels.
Cut the kernels from 1 ear corn into a bowl.
Add 2 tablespoons mayonnaise and stir thoroughly with a spatula, separating any clumps to ensure the individual kernels are coated.
Mix in 32 grams cake flour until the batter is sticky and begins to form clumps.
When you’re ready to fry, lightly oil your hands to prevent sticking. Shape the batter into ping pong ball-sized rounds, then gently lower them into the hot oil.
Fry the corn tempura, occasionally turning until golden brown and crispy, about 4 minutes.
Drain the finished tempura on the prepared rack and sprinkle with flaky salt to taste.