For the onion rings in cornflakes breading, first cut the onions into 4 slices each and separate the rings from each other. Use only the larger rings.
Crush cornflakes in a plastic bag, mix with salt, sugar and paprika powder. Beat egg until very creamy (best done with a food processor).
Bread the onion rings with egg and cornflakes. Spread evenly on a baking sheet (or sheets) lined with parchment paper.
Bake at 190 °C for about 15 minutes until the onion rings are crispy in cornflakes breading.
Here you can find the video for the recipe.