The greatest frustration with toasties is when the bread is burnt on the outside while the cheese inside has not melted. With the following approach you solve that problem. For the ultimate glossy crunch, bread that is nicely browned but not burnt, use mayonnaise instead of butter. It sounds crazy, but it really works! The oil in the mayonnaise gets hotter than butter and together with the egg it creates a nice, equal, crispy crust.