To make the caramel sauce, put the sugar in a pan over low heat and wait for the sugar to melt, without stirring, until it turns a light golden caramel color. You can move the pan around as the sugar melts, but don’t stir with a spoon, just move the pan. Pour the caramel sauce in the mold and move it around so that it covers the bottom and sides.
Tear the stale bread into cubes and soak in the milk.
Beat the eggs by hand and mix with the sugar, vanilla, and orange zest. This is when you would add in the raisins that have been rehydrated in hot water.
Combine the egg mixture with the soaked bread mixture.
When the caramel sauce hardens in the mold, add the entire mixture and cover the mold with foil.
In the Instant Pot® inner pot, add 2 cups water and insert the rack. Place the mold on the rack.
Close and lock the Instant Pot® lid, making sure the steam release handle is turned to Sealing. Press Pressure Cook and set time to 40 Minutes.
Let cool before unmolding. Even better the next day, as that gives it time to set more. Store in the refrigerator and serve topped with the caramel sauce.