Preheat oven to 335 degrees F.
Cut loaf of bread into 1" cubes and place in 8x8 baking dish.
To make custard, beat egg, butter, vanilla, and milk together in a bowl.
While mixing slowly add sugar to egg mixture.
Pour custard over bread in baking dish.
Press bread down into custard to ensure bread soaks up custard.
Baker 30 to 40 minutes until custard is set up.