Remove the label from the can and then open the can (trust me, it's easier to remove the label first). DO NOT LEAVE THE LID ON THE CAN! It's very dangerous to cook a sealed can in a pressure cooker.
Cover the can with tin foil, securing it as tightly as possible.
Place a trivet in the bottom of the Instant Pot and then place the foil-wrapped can on top. You do not want the can directly on the metal bottom because it gets very hot.
Carefully pour water into the Instant Pot along the side (don't pour on top of the can). The water needs to be halfway up the side of the can.
Lock the lid in place and close the steam valve. Pressure cook on HIGH for 40 minutes. Once the cycle is complete, quick-release the steam.
Carefully remove the can from the pot. It will be very hot and this is where the canning jar lifter will come in handy if you have one. Place the can on a cooling rack, remove the foil, and allow it to cool down for 20 minutes.
Stir the contents of the can with a spoon. Use a hand towel to hold the hot can. The caramel will be lumpy at first, keep stirring. Add the vanilla extract and salt (if making the salted version) and continue to stir until you have a smooth consistency. Transfer to a sealable container like a glass jar.
You can enjoy the dulce de leche immediately or store it in a sealed container in the fridge until you are ready to use it. The caramel will last for up to two weeks sealed in the fridge. The caramel will not harden but it will thicken when cold. Set it on the counter to warm up or zap it in the microwave for 10-15 seconds in a microwave-safe container.