In a heatproof bowl, combine the chocolate and coconut oil. Bring a small saucepan of water to a boil, and set the bowl on top, ensuring that it does not touch the water, but hovers just above it. Stir frequently until it has mostly melted. Remove from the heat and continue stirring until fully melted and smooth. Alternatively, heat the bowl in the microwave in 30 second increments, stirring in between until fully melted. Set the mixture aside and let it cool for 10 minutes.
In a large bowl, whisk together the eggs, vanilla extract, coconut sugar, maple sugar, almond flour, coconut flour, arrowroot powder, and salt. Then whisk in the cooled, melted chocolate mixture. Divide the batter among four 6-ounce jars. Gently top each jar with a piece of foil; do not seal it, just lay it over the top to prevent condensation.
To the pot of an electric pressure cooker add 2 cups of water and arrange the wire steaming rack over top. Place the jars on the rack and secure the lid on the machine. Set the valve to seal. Set the machine to high pressure for 14 minutes. Do a manual, quick release of the pressure by canceling the machine and turning the valve to vent. Check the cakes. If they are done on top, cracked, and have risen, carefully remove the jars from the pot and remove the foil from the tops. If they need more time (this depends on the model), return the lid and cook on high pressure another 3 to 5 minutes.
To make the fudge drizzle, heat the chocolate and coconut oil in the same bowl until smooth. Then, poke a hole in the top of each of the jar cakes and drizzle a tablespoon of chocolate sauce into the center. Serve warm.
To bake: Preheat oven to 350F. Lightly grease 4 oven-proof ramekins with coconut oil. Bake, uncovered, for 20 to 22 minutes, until a toothpick comes out mostly clean in the center.
Notes
Make it ahead: cakes will keep in the fridge for 10 days. Reheat in a warm oven for 15 minutes.