How to Make It
Using the saute function on an Instant Pot, heat olive oil until fragrant. Place the corned beef brisket into the pot and sear undisturbed for 5 minutes, or until browned on the bottom. Flip and repeat on the other side.
Pour the water into the pot and cover the brisket with pickling spices, from yellow mustard seeds to bay leaf. Lock the lid on and make sure the valve is turned to seal. Set to high and cook for 75 minutes.
When the time is up, carefully release the pressure. This might take up to 15 minutes. Remove the beef from the Instant Pot and set aside to rest.
Strain the remaining gravy through a fine-mesh sieve over a large bowl. Reserve ¼ cup broth and return to the Instant Pot with the potatoes. Secure the lid and pressure cook on high for 12 minutes.
In the meantime, heat the remaining tablespoon of olive oil in a small pan over medium heat. Add the kale and scallions and sauté 5 minutes, or until softened and fragrant.
When the cooking time ends, drain all the water from the bowl of the Instant Pot and use a potato masher or electric mixer to mash the potatoes. Add the milk and salt. Use a spatula to fold in the softened kale and scallions.
Transfer to a serving dish. Make a well in the center and fill with chunks or strips of the corned beef brisket. Sprinkle the black pepper on top and garnish with additional scallions or chives.