Drain them completely and pat them dry with a paper towel to remove excess moisture.

Put the black beans, banana, cocoa powder, maple syrup, vanilla extract and salt, if using, into a high-speed blender or food processor. Blend until completely smooth and creamy.

Line an air-fryer-safe brownie pan or silicone mold with parchment paper.

Pour the batter into the pan and smooth out the top with a spatula.

Place the pan into the air fryer basket. Cook at 330°F (165°C) for 15 to 17 minutes.

Insert a toothpick into the center. It should come out mostly clean with just a few moist crumbs. The top should look set and matte.

Let the brownies cool completely in the pan, then refrigerate for at least 1 hour before slicing. They will firm up significantly as they cool.