Scald the milk and cream in a heavy-bottomed saucepan (do not boil). Stir in the butter to melt. Set the pan aside to cool slightly.
In a mixing bowl, combine the beaten eggs, vanilla, sugar, and salt. Very gradually stir the warm milk into the egg mixture. Then stir in the bread cubes.
Butter a 2-quart baking dish and pour in the custard. Sprinkle with cinnamon and nutmeg. Set the dish inside a larger pan with ½ inch hot water in it.
Bake for 40 to 50 minutes or until the custard sets and a knife inserted near the center comes out clean.