Pour the sweetened condensed milk into the canning jar and cap with a lid and ring. Place the steamer insert/basket into the pressure cooker and place the jar on top of it. Fill the pressure cooker pot/insert until water comes up halfway on the jar (WARNING: consult the directions of your pressure cooker to make sure you don't overfill the pressure cooker with water; it will depend on the size of the pressure cooker).
Seal the pressure cooker.
For a stovetop model, bring the pressure cooker to high pressure and maintain high pressure for 50 minutes. Quick release when the time is up.
For the InstantPot, select Manual and then adjust the time up to 60 minutes. When the time is finished, quick release by pushing the valve to the Venting position to let out the steam.
Carefully remove the dulce de leche jar from the pressure cooker and let cool until just slightly warm before stirring (or else it will curdle).
Notes
Sweetened Condensed Milk: I have not tried this recipe with reduced fat or fat free sweetened condensed milk.Jars: also, I usually make two jars at once so if you are opposed to having half of a can of sweetened condensed milk left over, either a) use three cans and split them between two pint-size canning jars or b) only use one can of sweetened condensed milk (and cut down the time for pressure cooking accordingly). I haven't cooked two jars in my pressure cooker at once; while they will fit, I don't know how that will affect time. I'm guessing it will be pretty close to the same.Wait Until it Cools: don't stir the dulce de leche right when it comes out! Piping hot and that beautiful mess will curdle.