Heat oil in a heavy pot or deep fryer until it reaches a temperature of 350°F (180°C). Ensure it does not go above 1 1/2-inches.: You will hear a steady, gentle shimmer from the oil as it approaches frying temperature, and faint wisps of steam may rise. Using a thermometer is crucial because too cool and the nuggets absorb oil, becoming greasy, too hot and they brown on the outside before cooking through. A common mistake is crowding the pot, which drops the temperature suddenly; fry in small batches to keep the heat steady. Watch for small bubbling when a drop of batter is added, that indicates readiness and stability for frying.
Combine flour, baking powder, salt, and sugar in a medium bowl.: The dry mixture should smell faintly wheaty with a subtle sweet note from the sugar . Whisking aerates the flour and disperses the baking powder so nuggets rise uniformly. If you skip thorough mixing, you'll get uneven pockets of leavening or salty spots. Use a whisk and check that no lumps remain so the batter blends smoothly with the wet ingredients.
In a separate bowl, whisk the egg, milk, and shortening. Combine the wet mixture with the dry mixture. Fold through the corn.: The whisked wet mix will be glossy and fluid, and when you fold it into the dry ingredients the batter will thicken slightly while still remaining loose. As you fold in the corn , notice how the kernels distribute, creating little sweet bursts throughout the batter. Overmixing at this stage can make the batter gluey and dense, so fold gently until just combined. If the batter seems too stiff, add a splash more milk to reach a spoonable consistency.
Drop the nugget batter by spoonfuls into the hot oil. Fry for a minute on both sides until golden.: As each spoonful hits the hot oil , expect a lively sizzle and quick puffing as the exterior seals. After about a minute, use a slotted spoon to gently turn the nugget so the other side also browns evenly; you want an even deep golden color. If the sound becomes a loud crackle or smoke appears, the oil is too hot and you should lower the heat. One frequent error is flipping too soon, which can break the crust and let oil in, so wait until the edge holds its shape before turning.
Remove the nuggets from the oil and place them on a wire rack to drain excess oil before serving.: The aroma will be rich and toasty as you transfer the nuggets, and placing them on a wire rack keeps air circulating so they remain crisp. Using paper towels traps steam and can make the underside soggy, so I prefer a rack over a tray. A common misstep is piling them up; give each nugget space or they will steam each other and lose crispness. Let them rest briefly, about a minute or two, so the interior sets but they are still warm and tender when served.
