Grease your baking pan with a little oil or non-stick spray to prevent sticking. If you want, you can line the bottom with parchment paper for added assurance.
In a mixing bowl, sift together the all-purpose flour, granulated sugar, cocoa powder, baking powder, baking soda, and salt. Whisk them until evenly combined.
In another bowl, whisk together the almond milk, avocado oil, eggs, and vanilla extract until well blended.
Gradually pour the wet ingredients into the dry mixture, stirring gently until just combined. Be careful not to overmix, as this can lead to a dense cake.
Carefully stir in the boiling water. This will thin out the batter and create a more tender crumb. It might seem runny, but that’s exactly what you want!
Pour the batter into the prepared baking pan, smoothing out the top with a spatula.
Add 1 cup of water to the bottom of the Instant Pot. Place the trivet inside and set the baking pan on top of it.
Secure the lid on the Instant Pot and set it to cook on high pressure for 30 minutes. Once the cooking time is up, allow the pressure to release naturally for about 10 minutes before doing a quick release for any remaining pressure.
Remove the baking pan from the Instant Pot and check if the cake is done by inserting a toothpick into the center. If it comes out clean or with a few crumbs, your cake is ready!
Allow the cake to cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely. Once cooled, frost with your favorite chocolate frosting.