Add a cup of water to the instant pot and place a trivet inside. Make a sling using aluminum foil and place it inside the instant pot. Grease a 6-inch cake pan on the sides and bottom and keep it aside.
In a mixing bowl combine flour, cocoa powder, baking soda, coffee powder, and salt.
In another bowl beat sugar, egg, buttermilk, vanilla extract, and oil. Combine the dry and wet mixture until well combined.
Pour the batter into the greased pan and cover it with aluminum foil. Place the cake pan on the trivet and close the instant pot. Place the valve in the “sealing” position and press “manual” and set it to 35 minutes.
Once the cake is done release the remaining pressure after 15 minutes. Carefully remove the cake from the cake pan and allow it to cool.
Dust some cocoa powder on top of the cake and decorate it with berries. Serve the slice of cake with whipped cream on top.