In this recipe, the Instant Pot is being used as a self-contained steamer—not as a pressure cooker. So you need to leave the pressure valve set to Venting when cooking the custard. Do not seal it. I grew up watching my mother make this recipe in a stovetop pressure cooker. It was one of the first things I learned to make, when I was fourteen years old. It’s a lot lighter than a flan, which is how I justify eating a lot of it in one sitting!
In a medium saucepan, heat 5 tbsp of the sugar and the water over medium heat. Allow the sugar to caramelize without stirring (it will seize up if you stir it, especially once it’s started boiling). Cook until it is a deep, rich color, but do not let it burn. Quickly—and very carefully—pour the liquid caramel into a 6-inch soufflé dish that fits inside the Instant Pot.
In a medium bowl, whisk together the eggs, milk, remaining 1/4 cup sugar, and vanilla. Pour over the top of the hardened caramel; cover the dish with foil.
Pour 2 cups water into the pot. Place a trivet in the pot. Place the dish on the trivet.
Secure the lid on the pot. Set the pressure-release valve to Venting. Select SAUTÉ/NORMAL and set a kitchen timer for 22 minutes.
At the end of the cooking time, insert a toothpick in the center of the custard to check for doneness. The center will be jiggly, but the toothpick should come out clean.
Transfer the pan to the refrigerator to chill for 4 to 6 hours.
When ready to serve, use a knife to loosen the edges, place a plate on top of the dish, and invert the custard onto the plate. Thump the bottom of the dish if necessary. Top with berries, if desired, and serve.