Preheat the oven to 350°F with the rack in the middle of the oven. Grease and line with parchment an 8x10 baking dish. Set aside.
Place the cocoa powder in a medium heatproof bowl. Pour in boiling water and mix well to combine. Set aside to cool to room temperature.
In the bowl of a stand mixer using the paddle attachment, or a large bowl with a hand mixer, cream the shortening, butter, and sugar until light and fluffy, about 4 minutes.
Add the eggs and egg yolk one at a time, making sure to fulling incorporate each egg before adding the next one. Add the vanilla and mix.
In a medium sized bowl, sift together the gluten free flour, baking powder, baking soda, cinnamon, and salt. Add half the flour mixture and half the liquid cocoa. Mix well and add the final batch of flour and cocoa. Mix until the batter is smooth.
Pour batter into prepared pan and use a spoon or spatula to distribute it evenly in the pan. Bake the cake for about 28-30 minutes or until a toothpick inserted in the center comes out clean. Let cool completely before frosting.
To make this dairy free, swap out the butter with plant-based options that work for you! To ensure they are corn and soy free, make sure your gluten free flour blend does not contain any corn or soy. Also check your powdered sugar when making a frosting.To make cupcakes with this recipe:Line 2 muffin tins with cupcake liners (total 24). Fill cupcakes about ⅔ full. Bake in the oven at 350F for 22-24 minutes or until a toothpick inserted into the center pulls out clean. Let cool completely before frosting. LivingBeyondAllergies.com