Instructions

• Cut the 1/4 cup unsalted butter into cubes. Use a few cubes to butter the insides of your ramekins and set the buttered ramekins aside. If you want to dust the finished cakes, set aside a small amount of the 1/2 cup powdered sugar now; otherwise use all of it in the batter. Place the Instant Pot trivet inside the pot and add 1 cup water.
• In a medium heatproof bowl, combine the remaining butter cubes and the 4 oz. chocolate. Microwave in 15-second intervals, stirring between each interval, until the butter and chocolate are fully melted and the mixture is smooth. (Alternatively, melt over a double boiler.) Let the melted mixture sit 1–2 minutes to cool slightly so it is warm, not piping hot.
• Whisk the 1/2 cup powdered sugar (minus any small amount you set aside for dusting) and the 1/4 teaspoon espresso powder into the warm chocolate until thick and smooth.
• Whisk in the 1 large egg, the 1 egg yolk, and the 1/2 teaspoon vanilla extract until the mixture is fully combined. If the chocolate mixture feels very hot, temper the eggs by whisking a spoonful of the chocolate into the eggs first, then whisking the egg mixture back into the bowl.
• Add the 1/4 cup all-purpose flour and the 1/4 teaspoon salt. Fold them in with a spatula until just combined; do not overmix.
• Divide the batter evenly among your prepared ramekins. Place the filled ramekins on the trivet in the Instant Pot (arrange so they sit steadily).
• Close the Instant Pot lid and set the steam valve to the "Sealing" position. Cook on High Pressure for 8 minutes.
• When the cook time ends, press the "Cancel/Off" button and perform a quick pressure release carefully (keep your face and hands away from the steam).
• Open the lid, put on oven mitts, and carefully remove the ramekins from the Instant Pot.
• Run a thin knife around the inside edge of each ramekin to loosen the cake. Place a plate over a ramekin, invert the ramekin onto the plate, tap gently, and lift the ramekin off to release the cake. Let the cakes rest on the plate a minute to settle.
• If you set aside any powdered sugar, lightly dust the tops now. Serve the lava cakes warm.