Begin by zesting the lemons to gather the 4 teaspoons of lemon zest. Make sure to only use the yellow part of the peel, as the white pith can add bitterness. Next, juice the lemons until you reach 2 cups of fresh lemon juice.
In a mixing bowl, combine the lemon zest, lemon juice, sugar, softened butter, eggs, and egg yolks. Whisk everything together until it’s well combined and smooth.
Pour the lemon mixture into a heatproof glass jar or bowl that fits in your Instant Pot. Add one cup of water to the pot, place the trivet inside, and set the jar on top of the trivet. Lock the lid, set the valve to sealing, and cook on high pressure for 10 minutes.
Once the cooking time is complete, allow the pressure to release naturally for 10 minutes, then carefully perform a quick release to let out any remaining steam.
Remove the jar from the Instant Pot and allow it to cool slightly. For an ultra-smooth texture, strain the curd through a fine-mesh strainer into another bowl. This removes any bits of zest or coagulated egg that may have formed.
Transfer the strained lemon curd into a clean glass jar or airtight container. Allow it to cool completely before sealing and refrigerating.