Whisk the egg, Parmesan, paprika, mustard, Worcestershire sauce and milk together in a shallow dish that the slices of bread will fit in with not a great deal of space around them, making sure everything is completely combined.
Sit the bread in this mixture for about 2 minutes each side, pressing down on it every now and again. You want the slices to be soaked through and softened, but not falling to pieces. Spoon any remaining egg mixture over.
Warm the butter and oil in a frying pan in which the slices will sit fairly snugly. Once the butter is beginning to bubble frothily, fry the bread over a medium-high heat, turning it down if the butter gets too hot, for about 2 minutes each side until it is cooked through with patches of rich golden brown on the surface.
Remove from the pan, and eat just as it is, or sprinkle with chopped parsley and thinly sliced spring onion, if wished.