In a bowl, whisk the egg yolks together with the milk. Add the flour, the baking powder, the salt and the freshly ground black pepper. Use a whisk to mix everything together until smooth, then stir in the fresh or frozen sweetcorn, whichever you're using. In a separate clean, dry bowl, whisk together the egg whites with a pinch of salt, until they form stiff peaks, then carefully fold in the corn mixture - make sure not to fold too heavily to keep the air in the mixture.
Put a frying pan on a medium heat and add the 3 tablespoons of sunflower oil. If you're using a large frying pan, you may need to add more sunflower oil - it should completely cover the base of the pan.
When the oil is quite hot, spoon in a tablespoon of the fritter mixture and very lightly flatten it with the spoon if it's too lumpy. Cook for about 30 seconds to 1 minute on one side - the fritter should be golden and crusty - then use a spatula to turn it over, and cook for a further minute or so on the other side. Use a slotted spoon to remove the fritter and place it on kitchen paper to drain.
Repeat for the rest of the mixture. You can do more than one at once, but be careful not to overload the pan, or they'll fuse together! You'll need to add more sunflower oil every few batches. Serve the fritters with mango and avocado salsa.