Preheat oven to 350 (175 C) degrees with rack in the center.
Put the cream and chocolate in a small saucepan and bring to a simmer. Remove from the heat and stir until completely smooth.
Pour the chocolate mixture into an 8 x 2-inch round or square cake pan or baking dish and sprinkle the cacao nibs over.
Whisk the cocoa and boiling water in a large heatproof mixing bowl until incorporated. Add the eggs, coconut oil, coconut sugar and vanilla and whisk until smooth and the oil is emulsified.
Sift the almond flour, cinnamon, baking soda and salt through a mesh strainer set over a bowl. Whisk to combine.
Add the dry mixture to the chocolate mixture and stir to combine. Scrape into the baking pan.
Bake 30-35 minutes, or until the center of the cake feels set when touched with your finger.
Cool in the pan 10-15 minutes. Serve warm straight from the pan with whipped cream on the side. Sprinkle with cacao nibs and dust with cacao powder, if desired.
Notes
This cake will keep covered for a few days at room temperature. Warm it up in the microwave for about 15 seconds it you like.