Lightly grease an 8-inch square pan and line it with parchment paper. Leave enough length on both sides so you can easily use the extra paper as handles when removing the marshmallows from the pan.
In a small bowl, mix together the cocoa with arrowroot flour. Lightly sift half of this mixture into the bottom of the pan. Set aside.
In a small bowl, whisk together 3 tablespoons of water with cacao powder until a thick paste forms. This should only take 20-30 seconds. Add ½ cup of the remaining water into the bowl of a stand mixer. Sprinkle the powdered gelatin evenly over the water. Add in the cacao paste and mix on low to combine for 15 seconds. Turn off the mixer and leave the mixture to bloom.
In a large and tall saucepan, combine the remaining ½ cup of water, maple syrup, honey and salt. Bring the mixture to a boil over medium-high heat. Make sure you keep a close eye on it, as it tends to foam up pretty quickly. (This is why using a very tall saucepan is helpful!) Place a candy thermometer into the saucepan and continue boiling until the temperature reaches 240°F (114°C). This will usually take around 12-14 minutes after it first boils. Remove from heat, and immediately fit a whisk attachment to your stand mixer. Turn the mixer on medium-low speed, while simultaneously and steadily pouring in the syrup mixture. Make sure you cover all of the gelatin with it, so it can melt. After the syrup has been incorporated, turn the mixer up to high and continue beating until the mixture has more than doubled in volume. This will take anywhere between 6-8 minutes. To make sure they are done, turn off the mixer and lift up the whisk.The marshmallow cream should slowly fall off the whisk attachment. Beat in the vanilla extract until combined.
Transfer the marshmallow to the prepared square pan. Quickly smooth over the top with an offset spatula, making sure the top layer is even. Immediately sprinkle with a little more of the dusting mixture and crushed cacao nibs.
Leave the marshmallow cream uncovered in order to set for at least 3.5-4 hours. Alternatively, you can let them set overnight. Carefully lift the marshmallows, using the handles you created with the excess parchment paper, up and out of the baking dish. Cut them into your desired size. Add the rest of the dusting mixture to a colander and toss the marshmallows until they are lightly coated.
These will keep for a few days in an airtight container. If you aren't planning on eating all of them, freeze the excess for up to 1 month.