Peel the packaging off the condensed milk and place it into the Instant Pot inner pot. Pour over warm water until the condensed milk is submerged. Place the lid on the Instant Pot, set the valve to sealing and cook on manual for 40 minutes.
Place the caster sugar, risotto rice and whole milk into the Instant Pot. Place it on the sauté setting and bring to the boil. Make sure you stir constantly to prevent burning.Cancel the sauté once it has come to the boil.
The condensed milk should have had long enough to cool now. Remove the lid and give it a quick stir.Remove the lid on the Instant Pot after its extra 15 minutes and stir it a few times, adding the butter and the vanilla as you stir.