Preheat your air fryer to 370 degrees f. 

In a double broiler or a microwave-safe bowl, melt your chocolate. If you are using a microwave, melt the melted butter and the chocolate bar, broken into pieces, together at 30 second intervals making sure to stir after each interval. You will only need to do this a few times. Then set aside.

In another medium-sized bowl, using a whisk, stand mixer, or hand-held mixer, beat eggs, white granulated sugar, and pure vanilla extract. Only mix until the mixture becomes frothy. 

Pour the chocolate mixture into the egg mixture and stir together. Then slowly incorporate the all-purpose flour and kosher salt. Stir just until the mixture is combined. Do NOT overmix the batter. 

Lightly spray your ramekins with your favorite cooking spray. 

Pour the batter into the ramekins, approximately 2/3rds full. 

Place ramekins in the air fryer basket and check at 5 minutes. 

Test for doneness by looking at the sides of the cake. If there are starting to get crispy and the cakes have begun to pop up, then remove them from the air fryer using oven mitts or a thick dish towel. 

Let the lava cake sit for a few minutes, then invert them onto a plate. 

Dust with powdered sugar and serve with fresh berries, whipped cream or vanilla ice cream.