Combine the egg with a tbsp of mustard - a tbsp of mustard for each egg. Mix until homogenous.
Prepare three plates - flour/cornstarch, the eggs, and the breadcrumbs/cornflakes/chips.
Add salt or other spices to the breadcrumbs/cornflakes/chips.
Pat dry the food you wish to fry (steak, fish, chick breast).
Cover the food with a thin layer of flour, then egg and finely breadcrumbs. Make sure each has a thin layer, discard any excess breadcrumbs or egg.
Place the food on an oven baking sheet covered in baking parchment.
Place the baking sheet in a high rack in an oven preheated to 230°C (450°F), for ~15 minutes.