Preheat the oven to 450 degrees Fahrenheit. Make the frosting first.

Prick the sweet potatoes all over with a fork and place them on a small baking sheet lined with Gefen Parchment Paper. Roast for about 60 minutes, or until completely tender in the center.

Remove the sweet potatoes from the oven and set aside until cool enough to handle, about 10 minutes. Cut the skins open and scoop out the flesh. Measure two packed cups of flesh and transfer to the bowl of a food processor. Add the rest of the frosting ingredients and process for about 30 seconds, until a thick-and-creamy frosting forms. Scrape down the sides of the bowl and process again for another 10 seconds, or until smooth. Transfer to an airtight container to cool completely, then cover and place in the fridge for a minimum of four hours (or overnight) to set.

To make the cake, preheat the oven to 350 degrees Fahrenheit. Grease two (eight-inch) cake pans with avocado oil, and line the bottom of each with parchment paper.

In a medium bowl, whisk together the flaxseed and hot water and allow to thicken for about 15 minutes, stirring occasionally.

In a large bowl, combine and whisk together all the dry ingredients.

Add the remaining wet ingredients to the flaxseed mixture and whisk together well. Add the wet ingredients to the dry; using a spatula, mix everything well until a thick, smooth batter forms.

Divide the batter evenly between the two pans, using the back of a spoon to smooth out the surface of the batter. Bake on the center rack for 30 to 35 minutes, or until a toothpick inserted in the center comes out clean. Let the cakes cool in the pan for 30 minutes, then run a kitchen knife around the edges of each cake to loosen. Invert each cake onto a rack and peel off the parchment paper. Allow to cool completely, about two hours. If working ahead, wrap each cake layer individually and tightly in plastic wrap and store at room temperature until you are ready to assemble the cake.

To assemble the cake, transfer the first layer to a cake stand or a serving dish. Add half the chocolate frosting and spread it evenly over the cake with the back of a large spoon. Place the second cake layer on top of the frosted first layer and add the remaining frosting.

Serve the cake immediately or refrigerate until chilled, about four hours, before serving. Store any leftover cake in the fridge for up to three days, covered with plastic wrap, making sure to gently press the wrap against the surface of the cake to create an airtight seal.