Prepare 2 round 6" pans by lining the bottoms with parchment paper. Set aside.
Preheat oven to 325°F/163°C.
In a stand mixer bowl fitted with a paddle attachment, sift together the all-purpose flour, baking soda, baking powder, sea salt, sugar and cocoa powder.
Using a measuring cup, combine the avocado oil, buttermilk, boiling water and vanilla extract. Give it a stir to combine.
Gradually pour the liquid mixture into the dry ingredients, while the mixer is running on low. Increase the speed to beat the ingredients together, for about 30 seconds until smooth (don't overbeat).
Give the bowl a scrape and with the mixer on low, add 1 egg at at a time, and beat again until smooth, another 30-60 seconds.
Divide the cake batter evenly into 2 round 6" pans.
Give the pans a tap to release any trapped air bubbles.
Bake the cakes at 325°F/163°C for 30-35 minutes, or until a toothpick inserted comes out clean or with the slightest crumbs clinging to it.
Remove from the oven and cool on a wire rack for 15 minutes, before removing the cakes from the pans.