10 tablespoons unsalted high-fat butter, such as Plugra
1 cup semisweet (or bittersweet) chocolate chips
2 tablespoons Dutch-process cocoa powder, plus more for garnish
1/2 teaspoon fine sea salt
1/2 cup granulated sugar
1/2 cup light brown sugar
2 teaspoons pure vanilla extract
4 large eggs, at room temperature
Crème fraiche, for serving
Pour 1 cup water into the Instant Pot. Line a 7-inch springform pan (with removable bottom) with a parchment round and grease the sides and paper-lined bottom with cooking spray or softened butter.
Put the butter, chocolate, and cocoa powder in a medium-sized microwave-safe bowl and microwave on high in 40 second intervals, whisking after each, until melted. Or, place the butter, chocolate, and cocoa powder in a heat-proof bowl over a pot of simmering water and whisk until melted.
Add the salt and sugars to the warm chocolate and whisk to combine.
Add the vanilla and then the eggs one at a time, whisking gently after each, until combined.
Transfer the batter to the prepared pan and tap the pan against the counter to pop any air bubbles. You probably won't be able to pop them all (don't worry).
Cover the pan tightly with a sheet of tinfoil, making sure to tuck the edges of the sheet under the pan, and not on top. Place it on the Instant Pot trivet and using the long trivet handles, lower the cake into the pot.
Secure the lid and set the pressure release valve to sealing. Select Manual and set the cooking time for 50 minutes on high pressure. The pot will take about 5 minutes to come to pressure before the actual cooking time begins.
When the cooking program ends, let the cooker release naturally for 10 minutes and then move the pressure valve to venting and release the rest of the steam.
Open the pot and using potholders, or a dish towel, carefully grab the trivet handles and remove the cake. Although some recommend creating a tinfoil sling with which to remove items from the pot, I have never had trouble lifting out something hot, as long as I am using my long-handled trivet (the one that comes with the Instant Pot). But if you are nervous about burning yourself, just wait to remove the cake until it has cooled enough to easily handle.
Unwrap the tinfoil, being careful not to pour any of the collected condensation on the cake. The cake is ready if the center jiggles just slightly like firmly set jello. Blot the top with a paper towel to absorb any condensation. Let the cake cool to room temp on the counter, about 2 hours.
Remove the sides of the pan by running a paring knife around the edges. Then remove the bottom of the pan by sticking a long knife between the paper and the round metal bottom piece and shimmying it a bit until the cake releases. Garnish with cocoa powder and serve slices with dollops of crème fraiche.
The cake will keep wrapped in plastic wrap on the counter for up to 3 days. Or you can refrigerate it for up to a week or freeze it for up to a month (and late-night frozen slivers of this baby are some of life’s greatest pleasures, FYI).