Add the sesame oil garlic, ginger, and red pepper flakes to the cooker and sauté for a minute.
De-glaze with vinegar, mix in the sugar, soy sauce, and beef stock – mix well. Add the ribs to the cooker coating them with the mixture.
Close the lid and set the valve to the pressure position. Pressure cook on HIGH for 45 minutes if using a stovetop pressure cooker, or 60 minutes on HIGH if using an electric cooker.
When time is up, open the pressure cooker using the natural release method.
Remove the ribs from the cooker, leaving the cooking liquid inside, and place on an oven pan (they will not look very dark yet, this is ok). Slide under the broiler for about 5 minutes to brown (which will change their color to a rich dark brown).
In the meantime, make a slurry in a small bowl with the corn starch and water and then mix it into the rib cooking liquid in the cooker.
Boil the mixture in the cooker until it reaches the desired consistency and then pour over the ribs before serving.