Add chocolate and butter to a microwave-safe bowl and microwave on high. Stir every 15-20 seconds until fully melted. Let cool for 5 minutes.
In a large mixing bowl, whisk together the sugar, flour, cocoa powder, and salt.
Add the chocolate mixture and eggs and stir just combine using a rubber spatula. Set aside.
Grease four 6-ounce ramekins with butter and add cocoa powder. Shake ramekins until the inside of the ramekins is covered in cocoa. Spoon the batter into each ramekin, filling each one about ⅔ full.
Preheat your air fryer to 360°F (180°C). Once preheated, place the ramekins inside and cook for 8-10 minutes, or until the cakes are set but still slightly gooey in the center.
Remove the ramekins from the air fryer and allow them to cool for 1-2 minutes. The ramekins will be very hot! Run a butter knife around the edge of each ramekin to loosen the cakes, and then invert each one onto a plate.
Serve immediately while still warm with your favorite toppings.