Blend all ingredients together in a blender until smooth. Transfer to a heatproof liquid measuring cup or bowl and cover tightly with foil.
Place the trivet inside the Instant Pot or other electric pressure cooker. Add 1 1/2 cups water. Set the covered bowl of lemon curd on the trivet.
Secure the lid, set the valve to seal, and set the Instant Pot to pressure cook on high pressure for 10 minutes.
Let the pressure naturally release for 10 minutes (this is important for the curd to fully set up!), then quick release the remaining pressure.
Carefully remove the bowl from the pot. Remove the foil. It should be set like jello or custard. Whisk until creamy and smooth. (At first it will look curdled, but as you whisk, it will come together.) Optional: strain to remove the lemon zest.
Refrigerate until ready to use (it will thicken as it cools). If it splits or looks curdled after sitting, whisk again to recombine.
Double: this recipe can easily be doubled; it doesn't expand much while cooking so as long as the heatproof bowl fits in the Instant Pot, it should work. Update: I'd recommend adding 2-3 minutes to the cooking time for a doubled batch. Thicker Curd: this homemade lemon curd will likely be a bit thinner than storebought brands you are used to (especially since many of them contain thickeners like gelatin and cornstarch), but it will definitely thicken up as it cools in the refrigerator. For thicker curd you can also decrease the lemon juice to 1/3 cup OR try adding an extra egg yolk.Other Flavors: this recipe converts well to lime curd. I haven't tried it with other citrus fruits like orange or grapefruit, but I'm guessing it will work just fine.