Select "sauté" on the Instant Pot. Drizzle with oil. Once the oil is hot (the Instant pot should say "hot" or the oil will be shimmering) add the diced onion and salt. Cook until softened and turning golden, stirring occasionally, about 6 to 8 minutes.
Stir in the garlic and cook an additional 2 to 3 minutes, until aromatic. If needed, deglaze the pot with a splash of vegetable broth to remove any stuck on bits from the pot.
Add the chopped kale, all of the vegetable broth, and the black pepper. Close the Instant Pot and turn the vent to "sealing".
For kale that still has a bit of a "bite" to it, cook on high pressure for 3 minutes. Carefully do a quick pressure release. The kale is still vivid green with this method.
For tender stewed kale, cook on high pressure for 9 minutes. Carefully do a quick pressure release. The kale appears stewed and deeper green with this method.
Before serving, toss the kale with 1 tablespoon of lemon juice, ½ teaspoon lemon zest, and the optional red pepper flakes. Serve with a slotted spoon.
Video
Notes
This recipe uses one bunch of kale or 8 cups of chopped kale. One cup of kale usually yields about 1 ounce of kale. One bunch of kale generally yields 7 to 8 ounces of kale, including the stems. If using a bunch of kale, the stems can be omitted or included.
Best within 3 to 4 days. Let cool to room temperature before placing in a closed container and refrigerating.