Heat oven to 350°F. Grease 2 8-inch cake pans and line with parchment paper.
In a small bowl whisk together the 1 cup pure pumpkin puree, ½ cup coconut milk, 2 teaspoons vinegar, and 1 tablespoon pure vanilla extract.
In a medium bowl, sift together the 1 ¼ cups sorghum flour , ½ cup arrowroot flour, ⅔ cup unsweetened cocoa powder, 2 teaspoons baking powder, 1 teaspoon baking soda, and ½ teaspoon fine sea salt.
Place the ¾ cup dairy-free butter, 1 cup granulated sugar, and ½ cup brown sugar, in a large bowl and, using an electric mixer on medium speed, beat until light and fluffy.
Add the 4 eggs one at a time and beat until fully incorporated.
Add the flour mixture and coconut milk mixture to the sugar mixture, alternating, and beginning and ending with the flour mixture. Continue beating on medium until incorporated.
Pour batter into the prepared pans, place in the oven, and bake for 35-45 minutes, until a tester inserted in the middle comes out clean. Remove from oven, place on a rack, and cool in pan for 15 minutes, then turn out to cool completely. Let rest in fridge at least 30 minutes or overnight, covered in foil, in the fridge.
Make Frosting
In a saucepan, heat the 2 cups coconut cream until almost boiling. Place the 7 ounces bittersweet chocolate in a large bowl. Pour the heated cream over the chocolate, let sit a few minutes, then whisk to combine. Let mixture cool; you can place in the fridge to speed things up.
When cool, whip with an electric mixer as you would whip whipped cream. When the chocolate ganache is whipped, and cake is cooled, fill and frost the cake. Keep refrigerated until ready to serve.
Cake will last 5 days, covered, in the fridge.
Notes
Use a gluten-free flour mix. When I developed this recipe, I decided to do a simple combination of two gluten-free flours rather than use an all-purpose mix. However, you can absolutely use a 1:1 baking mix, or my homemade gluten free flour blend, for the sorghum and arrowroot flours. You'll need 210 grams of gluten-free flour.
Sorghum flour substitute. Try gluten free oat flour or brown rice flour instead of the sorghum flour if you wish.
Make it refined sugar-free. Substitute coconut sugar for the granulated sugar and brown sugar.
Use dairy. Don't need to keep dairy-free? It's so easy to use regular dairy in this cake! Just substitute in unsalted butter, whole milk, and heavy cream.
Rest the batter. Gluten-free batter needs a little rest so that the flours can properly hydrate before baking. Let the batter rest in the pans while the oven heats for a smoother crumb.
Bring ingredients to room temperature. Let the dairy-free butter and eggs sit on the counter for about 30 minutes before using them. This will help them to incorporate better into the batter.