For the cake, line the bottom of an 8-inch springform pan with parchment paper that has been trimmed to fit; lightly spray the inside of the cake pan with coconut oil.
Beat together the butter and erythritol, and then beat in the eggs, followed by the vanilla, espresso powder dissolved in warm water, and stevia glycerite.
Beat in the almond meal, cocoa powder, flaxseed meal, baking powder, salt, and baking soda.
Pour the batter into the prepared pan and spread it out evenly.
Place a metal trivet into the inner chamber of pressure cooker. Add 1 1/2 cups (355 ml) water. Cover the cake with aluminum foil (to prevent condensation from dripping in), and place it on top of the trivet.
Turn the pot on Manual, High Pressure for 30 minutes and then do a quick release.
Use potholders to carefully remove the cake and uncover it. Let it cool completely before frosting.
For the frosting, turn pressure cooker on, press “Sauté”, and wait 2 minutes for the pot to heat up. Add the chocolate, cream, and butter, and cook just until melted, stirring constantly. Transfer to a bowl and set aside. Press “Cancel” to stop sautéing. Whisk in the Swerve Confectioners, vanilla, stevia glycerite, and salt until smooth. Let it cool to room temperature, stirring occasionally (it will thicken as it cools), and then refrigerate slightly until it’s spreadable like frosting.
Frost the cake, and decorate with berries if desired.